Crowds of school pupils protested in Sudan's main port city on Monday over spiralling food prices, witnesses said, as the country's economy languishes under a foreign currency crunch.

"Stop this hunger, we want food prices to fall," the pupils chanted as they headed towards government headquarters in Port Sudan, a key site of protests during the uprising that led to the ouster of former leader Omar al-Bashir last April.

Witnesses said groups of pupils planned to demonstrate in front of the governorate of Port Sudan, the capital of Red Sea state.

In December 2018, rising food prices including an over-night tripling in the cost of bread, along with general economic woes, triggered the uprising against Bashir which finally led to his ouster by the army in April.

Port Sudan, the African country's main economic hub, saw regular protests against Bashir's regime during the uprising.

The months-long demonstrations prompted the military to oust Bashir, ushering in the beginnings of a transition to civilian rule in August with a deal signed between generals and protest leaders.

But the country's economy continues to languish, severely hit by inflation and shortage of foreign currency.

On Monday, the Sudanese pound fell to 97 against the US dollar on the black market -- compared to an official rate of just 47 pounds to the greenback.

Sudan's transitional government has prioritised turning around the dilapidated economy and bringing peace to various conflict zones.

Prime Minister Abdalla Hamdok's administration is planning a host of economic reforms, including scrapping fuel subsidies, a major burden on the country's finances.