Black smoke hung over the Sudanese capital and tear gas stung the air on Friday as security forces tried to disperse widening protests sparked by rising food prices, witnesses said.
Numerous demonstrations were held throughout Khartoum and other cities, in the most serious expression of discontent since student-led protests began a week ago.
"People want to overthrow the regime!" protesters in a southern part of the city shouted into the early evening, an AFP reporter said.
"No, no, to high food prices!" they chanted elsewhere.
Burning tyres formed a cloud of thick smoke just before sunset over another neighbourhood, Al Deim, where protesters armed with stones gathered in small groups in the face of hundreds of security personnel who fired tear gas.
A police vehicle was also on fire in the area, a witness said.
"Police controlled small demonstrations in different areas of Khartoum state," a police statement issued through the official SUNA news agency said.
"Protesters destroyed a police car and police were forced to use tear gas against the demonstrators."
The statement said nobody was injured in the unrest and urged people "not to listen to rumours".
Demonstrations briefly touched the upscale district of Khartoum Two, home to business magnates and foreign embassies, where an AFP reporter saw tyres burning and said police fired tear gas.
Police also clashed with protesters in Khartoum's twin city of Omdurman, where about 200 demonstrators rhythmically clapped and shouted for "freedom," the reporter said.
Hundreds of people, mainly from the opposition Umma Party, separately gathered in Omdurman to call for regime change, a demonstrator there said. The crowd hurled stones while police used batons against them, he added.
"It's not only students" who have taken to the streets, said Latif Joseph Sabag, a member of the Umma Party's political bureau.
"These protests are expected because of the increase in prices and inflation, and so on," he told AFP. "The economic situation in Sudan is very bad."
Sabag said "nobody can tell" how much larger the protests might grow but his party was trying to talk to the ruling National Congress Party and suggest ways to "try to solve the problems and improve the situation in a peaceful way."
Inflation has risen each month, hitting 30.4 percent in May, before Finance Minister Ali Mahmud al-Rasul on Wednesday announced the scrapping of fuel subsidies, causing an immediate jump in petrol, cooking gas and other fuel prices.
Bankrupt Sudan has lost billions of dollars in oil receipts since South Sudan gained independence last July leaving the north struggling for revenue, plagued by inflation, and with a severe shortage of dollars to pay for imports.
The country's poverty rate is 46.5 percent, the United Nations says.
Outside the capital, witnesses in Sennar, the capital of Sennar state, said police fired tear gas and used batons when up to 300 people shouted against rising prices on Friday afternoon.
Residents in El Obeid, the capital of North Kordofan state, and in Wad Medani, the main centre in El Gezira state, also reported anti-regime protests.
Riot police have violently dispersed a string of protests since they began on June 16 outside the University of Khartoum.
London-based rights group Amnesty International on Friday urged Sudanese authorities to end "the ruthless crackdown on protests" and harassment of journalists reporting the events.
A correspondent for the international news wire Bloomberg said she was detained by state security agents for five hours while trying to cover a student protest on Thursday.
Salma El Wardany, an Egyptian, was held a day after AFP correspondent Simon Martelli, a Briton, was released following more than 12 hours in custody without charge.
University students have historically been in the forefront of opposition movements in Sudan, including in 1964 when protests led to a mass uprising that toppled the military dictatorship then in power.
The current regime of President Omar al-Bashir, an army officer who seized power in 1989, withstood earlier student-led protests by thousands objecting to high prices in 1994.
Sudan's latest demonstrations remain small compared with the mass uprising that swept neighbouring Egypt last year and toppled another long-time strongman, Hosni Mubarak.