Stepping up its crackdown on spiralling pro-independence protests by Tibetans, China has arrested over two dozen people and claimed that 170 others had "surrendered" as it rushed more troops to the restive Tibet and nearby provinces where agitators attacked shops and government buildings.

For the first time since riots erupted in Lhasa on Friday claiming 13 lives in the worst ever protests against its rule in two decades, China said Tibetan inhabited areas of Sichauan and Gansu provinces were too hit by the unrest.

Shops and government offices were attacked in the Aba county on Sunday and a similar scene was replicated in counties of Xiahe, Magu, Lugu and Jone and Hezuo city in the Gannan Tibetan Autonomous Prefecture in southern Gansu.

The riots were "closely linked" with Lhasa, Zhang Yusheng, a spokesman with the Gansu provincial government was quoted as saying by official Xinhua news agency on Wednesday night.

Ratttled by the protests, China has ordered its "largest mobilisation" since the unrest began, the BBC reported adding, 400 troop carriers and other vehicles were seen on the main road.

Two dozen suspects had been arrested in Lhasa for "endangering national security", looting, arson and "other grave crimes", the state-run Tibet Daily reported on Thursday.

Tibet regional government said 170 peeple had "surrendered" and most of them have admitted to committing minor offences, Xinhua said.

Authorities had asked rioters to surrender by midnight of Monday promising leniency and warning of harsh action against whose who failed to do so.