At least eight people have been killed in protests that have swept across Sudan for a second consecutive day amid rising public anger over soaring prices and other economic woes.

Authorities on Thursday declared a state of emergency in the eastern city of Gadarif, where six protesters died during clashes with riot police, legislator Al-Tayeb al-Amine Tah told local broadcaster Sudania 24 on Thursday, without providing further details.

"The situation in Qadarif has become dangerous and the protests have developed to include fires and theft and it's now out of control," Mubarak al-Nur, its independent member of parliament, told Reuters news agency.

Two protesters were also killed in the northeastern city of Atbara, where police fired tear gas to disperse demonstrators.

Authorities also imposed a curfew on the city after protesters torched the headquarters of President Omar al-Bashir's National Congress Party (NCP).

"The protests began peacefully and then turned to violence and vandalism ... We declared a state of emergency and a curfew and the closure of schools in the city," Hatem al-Wassilah, the governor of the Nile River state.

Residents told Al Jazeera that the protests were triggered on Wednesday by a government decision to raise bread prices from one Sudanese pound ($0.02) to three Sudanese pounds ($0.063).

Police on Thursday fired tear gas to break up a crowd of around 500 people in the capital, Khartoum, then chased them through back streets and made arrests, a witness said.

Some of the demonstrators called for the "fall of the regime", a slogan that was common during the Arab Spring uprisings that swept through the region in 2011. Police said "limited" protests in Khartoum had been contained.

On Friday, a spokesperson for the Sudanese government said the protests of the two previous days were "dealt with in a civilised way without repression or opposition".

"Peaceful demonstrations were derailed and transformed by infiltrators into subversive activity targeting public institutions and property, burning, destroying and burning some police headquarters," the spokesperson was quoted as saying to the official Sudan News Agency.

"The crisis is known to the government and is being dealt with."

Prices triple

Anger has been rising in the country over the rising costs of bread and fuel and other economic hardships, including skyrocketing inflation and limits on bank withdrawals.

Sudan's economy has struggled to recover from the loss of three-quarters of its oil output - its main source of foreign currency - since South Sudan seceded in 2011, keeping most of the oilfields.

The country's economic woes have been exacerbated in the past few years, even as the United States lifted 20-year-old trade sanctions on Sudan in October 2017. Washington has kept Sudan on its list of state sponsors of terrorism, which prevents Khartoum from accessing much-needed financial aid from institutions such as the International Monetary Fund and the World Bank.

Bread prices have more than tripled since the start of this year after a government decision to stop state-funded imports of wheat.

Officials had hoped the move would create competition between private companies importing wheat, and therefore act as a check on price rises - but a number of bakeries have since stopped production, citing a lack of flour.

This forced the government to increase flour subsidies by 40 percent in November.

Meanwhile, the value of the Sudanese pound has slumped by 85 percent against the US dollar this year, while inflation soared to nearly 70 percent in September.

In October, Sudan sharply devalued its currency from 29 pounds to the dollar to 47.5 after a body of banks and money changers set the country's exchange rate.

The move led to further price increases and a liquidity crunch, while the gap between the official and black market rates has continued to widen.

The economic crisis is one of the biggest tests faced by al-Bashir, who took power in a coup in 1989. 

In recent months, he has dissolved the government, named a new central bank governor and brought in a package of reforms, but the moves have done little to improve the situation.

In a separate development on Wednesday, leading opposition figure Sadiq al-Mahdi returned to the country after nearly a year in self-imposed exile.

Mahdi was overthrown in 1989 by a group of military commanders close to President Omar Hassan al-Bashir's National Congress Party.

"The regime has failed and there is economic deterioration and erosion of the national currency's value," Mahdi, who heads the Umma party, told thousands of his supporters.

His party has argued that Bashir must go in order to improve the country's image abroad and attract crucial investment and aid.