Hong Kong Cable TV reported that about 200 military vehicles, each carrying 40 to 60 armed soldiers, drove into Lhasa on Sunday.
Footage showed streets in Lhasa were mostly deserted with only armoured and military vehicles patrolling.
Loudspeakers on the streets repeatedly broadcast slogans urging residents to "discern between enemies and friends, maintain order".
Another slogan called on them to "Have a clear stand to oppose violence, maintain stability".
Witnesses and officials confirmed that residents were being ordered to stay off the streets.
"It is fairly quiet this morning. The police are patrolling the streets. The local people have been persuaded not to go out," a man at the Lhasa city government office said.
A Lhasa resident who refused to give her name said "the police told us not to leave our homes".
The violence erupted on Friday just two weeks before China's Olympic celebrations kick off with the start of the torch relay, which will pass through Tibet.
Chinese officials confirmed that 10 people had died in the violence, but others including exiled Tibetan leaders said the death toll was as high as 80.
China's communist government is hoping Beijing's hosting of the Olympics in August will boost its popularity at home as well as its image abroad.
But the event already has attracted scrutiny of China's human rights record and its pollution problems.
International criticism of the crackdown in Tibet so far has been mild without any threats of an Olympic boycott or other sanctions.
Calls for restraint
Condoleezza Rice, the US secretary of state, called on China "to exercise restraint in dealing with the protests", while the state department issued a travel alert for Americans in the region.
Rice said she was "concerned by reports of a sharply increased police and military presence in and around Lhasa".
Her statement called for China to release monks and others jailed for protesting.
International Olympic Committee president Jacques Rogge said he opposed an Olympic boycott over Tibet.
"We believe that the boycott doesn't solve anything," Rogge told reporters on the Caribbean island of St Kitts.
"On the contrary, it is penalising innocent athletes and it is stopping the organisation from something that definitely is worth organising."
A meeting of the standing committee of the Tibet Communist Party, the ruling body in Tibet, said efforts had to be made "to expose and criticise the evil acts done by the hostile forces and expose the ugly feature of the Dalai (Lama) clique".
In a statement on the Tibet Daily website, the group urged swift action against Tibet's independence movement.
It said the government should "unite all forces that can be united to wage a people's war against anti-splittism and to maintain stability".
On Sunday, the 11th Panchen Lama Gyaincain Norbu condemned the riot in Lhasa, saying the sabotage acts run counter to the Buddhism tenets.
Norbu, Beijing's choice as the reincarnation of the second highest ranking Buddhist figure, said the rioters' acts "not only harmed the interests of the nation and the people, but also violated the aim of Buddhism.
Lhasa is a sprawling city, and the security clampdown seemed to vary in different parts of the city.
A worker at one hostel in the city said the staff were not allowed to leave and they were running out of food.
"There are hundreds of soldiers outside and they will not let us go. There is a market next to our hostel and we have been sneaking in to get a few packets of instant noodles," she said, refusing to give her name.
But a clerk at a Lhasa hotel away from the area where the worst violence took place said nearby shops were open and guests were allowed to leave.
Feng Zhengjie, a major-general of the People's Liberation Army, told reporters in Beijing outside the National People's Congress that the government needed to pay "high attention to this sort of violent action".
"I hope and believe that the local government will handle this matter. It reminds all of us we need to pay attention to internal and external anti-China forces. Nowadays in society and internationally, there are people who don't want China getting strong," he said.
Even as Chinese forces appeared to reassert control in Lhasa, sympathy protests had erupted on Saturday in an important Tibetan town in Gansu Province.
Police fired tear gas to disperse hundreds of Buddhist monks and other Tibetans after they marched from the historic Labrang monastery and smashed windows in the county police headquarters in Xiahe, witnesses said.
On Sunday, Xushou Sheng, Gansu provincial governor, called the protests "a planned and organised destructive activity" and blamed the "outside Dalai group" for instigating the riots.
The unrest in Tibet began last Monday on the 49th anniversary of a 1959 uprising against Chinese rule of the region.
Tibet was effectively independent for decades before communist troops entered in 1950.
The protests by Buddhist monks spiralled to include cries for Tibet's independence and turned violent when police intervened.
Pent-up grievances against Chinese rule came to the fore, as Tibetans directed their anger against Chinese and their shops, hotels and other businesses.
The details emerging from witness accounts and government statements suggested Beijing was preparing a methodical campaign - one that if carefully modulated would minimise bloodshed and avoid wrecking Beijing's grand plans for the Olympics.
Law-enforcement agencies in Lhasa issued a notice offering leniency for demonstrators who surrender before the end of Monday and threatening severe punishment for those who do not.