The Chinese security forces have launched a "strike hard campaign" ahead of the second anniversary of riots and protests in Tibet against Chinese rule.
Special police detachments are stationed across the regional capital, Lhasa. Press reports say they have seized guns, ammunition and knives.
Police are also checking identity papers and searching homes.
The 2008 protests were the biggest show of anger by Tibetans against Beijing for two decades.
According to one person in Lhasa, police sweeps begin at dusk and go on into the night.
The situation across Tibetan areas has been tense since riots and protests broke out in March 2008.
China's leaders blame the exiled Dalai Lama, the head of Tibetan Buddhism, for orchestrating the unrest.
That is something he denies.
A few days ago, he said China's goal was to annihilate Buddhism in the Himalayan region. He said monks and nuns were being kept in prison-like conditions.
China and Tibetans who have fled their homeland have very different visions of how the region should be governed.
The two sides have been talking for years but - on the anniversary of this particular unrest - there seems little chance they will be able to reconcile their differences.