Thousands of Sudanese demanded the removal of a local police chief on Tuesday, witnesses said, on the third day of unrest sparked by an attack on a female student.

Crowds in Abu Hamad, about 500 kilometres (300 miles) north of Khartoum, "started a sit-in near the main court," one witness told AFP.

They were demanding that the town's top police officer and the head of the local government resign, residents said, adding that they community was fed up with what they perceived as a lack of action against migrants from other parts of Sudan who commit crimes in the area.

The migrants are working in the area's wildcat gold mines.

Unrest began after Sunday's attack on the young woman, which led crowds to burn the local market, the residents said.

Police said the woman was the victim of a beating and attempted rape at the campus residence of Nile State University.

They fired tear gas on Sunday, and again on Monday when about 2,000 people held a further protest as officials tried to negotiate, said the witnesses.

Production from wildcat gold mines has become a key revenue source for the cash-strapped Sudanese government.

Protests over local grievances occur frequently in Sudan but are often suppressed by police and state security agents.

Thousands took to the streets in late September, mostly in Khartoum, after the government slashed fuel subsidies. Demonstrators called for the overthrow of President Omar al-Bashir's regime, in the worst urban unrest of his 24-year rule.

Amnesty International said security forces were suspected of killing more than 200 protesters, many of whom were shot in the head or chest.

The government gave a toll of less than 100, and said it had to intervene when crowds turned violent, attacking petrol stations and police facilities.