As calm returned to Longnan in Gansu province, authorities said they had questioned 110 people over the riots that saw people throwing stones, bricks and bottles to attack police, according to a local government statement.

'Currently we have already detained 30 people (seven of these have been bailed pending further investigation), and 80 people have signed confessions, which vigorously frightened other criminals,' the statement said.

The government said the protest was triggered on Monday by about 30 people whose houses had been demolished to make way for a new government building, in an apparent typical 'land grab' case that often leads to protests in China.

The protest swelled to about 2,000 people on Tuesday, but had been stamped out by the evening amid a strong security presence and a lockdown on traffic.

Among the 74 people injured - armed and regular policemen, and three journalists - 11 were in hospital, according to the statement.

Demonstrations are common in China, often fuelled by government-backed land grabs or other types of abuse of power.

But as the global economic slowdown hits China and thousands of workers are laid off, the Communist Party is becoming increasingly concerned that any protest might escalate into broader unrest and form a challenge to its rule. -- AFP