Hundreds of protesters have rallied in Sudan's capital as riot police deployed heavily to prevent a planned march on President Omar al-Bashir's palace to call for his resignation following days of deadly demonstrations.

Angry crowds have taken to the streets in a dozen cities across the economically troubled country since Wednesday, after the government tripled the price of bread.

Police vehicles and officers armed with batons could be seen around the capital Khartoum as authorities braced for a further challenge to Bashir's decades-long rule.

In downtown Khartoum, police fired tear gas at the protesters who were chanting "Freedom, peace, justice and revolution is the people's choice".

Sudanese authorities say eight protesters have been killed in clashes since Wednesday, but Amnesty International has put the death toll at 37.

A troika of countries - Britain, Norway and the United States - along with Canada voiced "concern" over the violence in Sudan, the British embassy in Sudan said on Twitter.

It cited "credible reports" on "the use of live fire by the government of Sudan and of multiple deaths during several protests".him to the city of Wad Madani.

Doctors in Sudan went on strike yesterday and the group bringing together professionals from different sectors pledged to submit a demand for Mr Bashir's resignation at today's demonstration.

Mr Bashir, who has been in power since a 1989 coup, sought to damp down the discontent by vowing to "take real reforms" to solve Sudan's economic woes.

But his statements appear to have done little to appease the protesters angered over economic hardship.

Sudan is mired in economic difficulties including an acute foreign currency shortage and soaring inflation.

The crisis has worsened despite the lifting of an economic embargo by the United States in October 2017.

Inflation is running at close to 70% and the Sudanese pound has plunged in value, while shortages in bread and fuel have been reported across several cities including Khartoum.

Since the start of the protest movement, Sudanese authorities had arrested several anti-government figures with liberal and communist backgrounds.