China is deploying its largest navy fleet in regional waters in nearly three decades, posing a threat to Taiwan that is more pronounced than previous Chinese war games, the Taiwanese defence ministry said on Tuesday.

Speaking in Taipei, defence ministry spokesperson Sun Li-fang said the scale of the current Chinese naval deployment in an area running from the southern Japanese islands down into the South China Sea was the largest since China held war games around Taiwan ahead of 1996 Taiwanese presidential elections.

China's military has yet to comment and has not confirmed it is carrying out any exercises, Reuters reported.

China, which views democratically governed Taiwan as its own territory over the island's rejection, had been expected to launch drills to express its anger at President Lai Ching-te's tour of the Pacific that ended on Friday, which included stopovers in Hawaii and the U.S. territory of Guam.

Taiwan's military raised its alert on Monday after saying China had reserved airspace and deployed naval and coast guard vessels.

"The current scale is the largest compared to the previous four," Sun said. "Regardless of whether they have announced drills, they are posing a great threats to us."

Senior ministry intelligence officer Hsieh Jih-sheng told the same press conference there have so far been no live fire drills in China's seven "reserved" air space zones, two of which are in the Taiwan Strait, but there had been a significant increase in Chinese activity to the north of Taiwan over the last day.

The number of China navy and coast guard ships in the region, which a Taiwan security source told Reuters remained at around 90, was "very alarming", and China was taking aim at other countries in the region and not only Taiwan, he added.

China's deployment in the First Island Chain - which runs from Japan through Taiwan, the Philippines and on to Borneo, enclosing China's coastal seas - is aimed at area denial to prevent foreign forces from interfering, Hsieh said.

Syria's former president Bashar al-Assad is in Moscow with his family after Russia granted them asylum on humanitarian grounds, a Kremlin source told Russian news agencies on Sunday, and a deal has been done to ensure the safety of Russian military bases.

Russia's Foreign Ministry said earlier that Assad had left Syria and given orders for a peaceful transfer of power, after rebel fighters raced into Damascus unopposed on Sunday, ending nearly six decades of his family's iron-fisted rule.

"Syrian President Assad of Syria and members of his family have arrived in Moscow. Russia has granted them asylum on humanitarian grounds," the privately-owned Interfax news agency and state media quoted the unnamed Kremlin source as saying.

Interfax cited the same Kremlin source as saying Russia favoured a political solution to the crisis in Syria, where Moscow supported Assad during the long civil war.

The source said negotiations should be resumed under the auspices of the United Nations.

Mikhail Ulyanov, Russia's ambassador to international organisations in Vienna, said on his Telegram messaging channel: "Breaking news! Bashar al-Assad and his family in Moscow. Russia does not betray friends in difficult situations."

Syrian opposition leaders had agreed to guarantee the safety of Russian military bases and diplomatic institutions in Syria, the source told news agencies. But some Russian war bloggers said the situation around the bases was extremely tense and the source did not say how long the security guarantee lasted.

Moscow, a staunch backer of Assad whom it intervened to help in 2015 in its biggest Middle East foray since the Soviet collapse, is scrambling to salvage its position. Its geopolitical clout in the wider region and two strategically-important military bases in Syria are on the line.

A deal to secure Russia's Hmeimim air base in Syria's Latakia province and its naval facility at Tartous on the coast would come as a relief to Moscow.

The Tartous facility is Russia's only Mediterranean repair and replenishment hub, and Moscow has used Syria as a staging post to fly its military contractors in and out of Africa.

Losing Tartous would be a serious blow to Russia's ability to project power in the Middle East, the Mediterranean and Africa, say Western military analysts.

Military presence in doubt 

Influential Russian war blogger "Rybar", who is close to the Russian Defence Ministry and has over 1.3 million followers on his Telegram channel, said the situation around the bases was a serious cause for concern whatever Moscow's official line.

"Russia's military presence in the Middle East region hangs by a thread," Rybar said.

"What anyone decided in high offices is absolutely irrelevant on the ground," he added, suggesting Russian forces at the bases had not taken the initiative to defend their positions in the absence of orders from Moscow.

Russian warships had left Tartous and taken up position off the coast for security reasons, the Hmeimim airbase had effectively been cut off after rebels took control of a nearby town, Kurdish forces had started to block Russian facilities beyond the Euphrates, and Russian positions at an oil facility in Homs had been blocked, Rybar said.

Reuters could not independently confirm Rybar's assertions.

Earlier on Sunday, the Russian Foreign Ministry said in a statement that the two military facilities had been put on a state of high alert, but played down any immediate risk.

"There is currently no serious threat to their security," the ministry said as it announced Assad's departure from office and from Syria.

"As a result of negotiations between B. Assad and a number of participants in the armed conflict on the territory of the Syrian Arab Republic, he decided to resign from the presidency and left the country, giving instructions for a peaceful transfer of power," it added, saying Russia did not participate in those negotiations.

The Foreign Ministry said Moscow was alarmed by events in Syria.

"We urge all parties involved to refrain from the use of violence and to resolve all issues of governance through political means," its statement said.

"In that regard, the Russian Federation is in contact with all groups of the Syrian opposition."

Syrian rebels said Damascus was "now free of Assad," Reuters reported.

Earlier Assad flew out of Damascus for an unknown destination on Sunday, two senior army officers told Reuters, as rebels said they had entered the capital with no sign of army deployments.

Thousands in cars and on foot congregated at a main square in Damascus waving and chanting "Freedom", witnesses said.

"We celebrate with the Syrian people the news of freeing our prisoners and releasing their chains and announcing the end of the era of injustice in Sednaya prison," said the rebels.

Sednaya is a large military prison on the outskirts Damascus where the Syrian government detained thousands.

A Syrian Air plane took off from Damascus airport around the time the capital was reported to have been taken by rebels, according to data from the Flightradar website.

The aircraft initially flew towards Syria's coastal region, a stronghold of Assad's Alawite sect, but then made an abrupt U-turn and flew in the opposite direction for a few minutes before disappearing off the map.

Reuters could not immediately ascertain who was on board.

The head of Syria's main opposition group abroad Hadi al-Bahra Syrian on Sunday also declared that Damascus is now "without Bashar al-Assad".

Just hours earlier, rebels announced they had gained full control of the key city of Homs after only a day of fighting, leaving Assad's 24-year rule dangling by a thread.

Thousands of Homs residents poured onto the streets after the army withdrew from the central city, dancing and chanting "Assad is gone, Homs is free" and "Long live Syria and down with Bashar al-Assad".

Rebels fired into the air in celebration, and youths tore down posters of the Syrian president, whose territorial control has collapsed in a dizzying week-long retreat by the military.

The fall of Homs gave the insurgents control over Syria's strategic heartland and a key highway crossroads, severing Damascus from the coastal region that is the stronghold of Assad's Alawite sect and where his Russian allies have a naval base and air base.

Homs' capture is also a powerful symbol of the rebel movement's dramatic comeback in the 13-year-old conflict. Swathes of Homs were destroyed by gruelling siege warfare between the rebels and the army years ago. The fighting ground down the insurgents, who were forced out.

Hayat Tahrir al-Sham commander Abu Mohammed al-Golani, the main rebel leader, called the capture of Homs a historic moment and urged fighters not to harm "those who drop their arms".

Rebels freed thousands of detainees from the city prison. Security forces left in haste after burning their documents.

Syrian rebel commander Hassan Abdul Ghani said in a statement early Sunday that operations were ongoing to "completely liberate" the countryside around Damascus and rebel forces were looking toward the capital.

In one suburb, a statue of Assad's father, the late President Hafez al-Assad, was toppled and torn apart.

Outside the city, rebels swept across the entire southwest over 24 hours and established control.