Tens of thousands of protesting Nigerians defied an order to end a three-day-old strike on Wednesday as unions threatened oil production and a mob rampaged in one city, leaving a police officer dead.
The strike over soaring fuel prices sank Africa's largest crude producer further into crisis, with deadly religious violence, including four Christians gunned down on Wednesday, sparking warnings of a looming civil war.
The tensions have left the global oil market watching anxiously and President Goodluck Jonathan facing his toughest challenge since he was elected last year.
Despite a government order on Tuesday that labelled the strike illegal and threatened to withhold pay, protesters took to the streets as gangs of youths burnt tyres and harassed drivers for cash.
Pockets of Lagos, the largest city in Africa's most populous nation, descended into chaos, including one upscale neighbourhood, with gangs attacking a police car with sticks and ripping down signposts.
The main groups of protesters in Lagos however remained peaceful, with some 10,000 people at one of the largest demonstrations dancing and singing anti-government songs. Some vowed they would begin camping out there.
"I am here with my water and toothbrush because we are not leaving this arena until our demand for fuel at 65 naira (USD 0.40) is met," said Akinola Oyebode, a 23-year-old at the main protest in Lagos.
He was referring to the price of a litre of petrol before government subsidies were controversially scrapped from January 1.
"We shall not be intimidated by the police because our protest is legitimate and constitutional."
In the central city of Minna, a mob went on the rampage, burning political offices, leaving a police officer dead and prompting an all-day curfew. The cause of the violence was not immediately clear.
In Kano, the largest city in the north, a massive crowd thought to be in the tens of thousands marched through the streets.
Protesters and police had clashed in Kano on Monday, leaving at least two people shot dead, but no incidents were reported on Wednesday .
Oil production has so far not been affected by the strike, but workers threatened action if the government does not respond to their demands.
"We hereby direct all production platforms to be on red alert in preparation for total production shutdown," PENGASSAN union president Babatunde Ogun said in a statement as union officials met in the oil hub of Port Harcourt.