Buildings have been set aflame and there are reports of gunfire in Nigeria's biggest city after demonstrators were shot at a protest.
Rights group Amnesty International said at least 12 people were killed when soldiers opened fire in Lagos on Tuesday.
Authorities have imposed an indefinite round-the-clock curfew on the city and elsewhere, but some defied the order.
Protests against a police unit have been taking place for two weeks.
Demonstrators have been using the social media hashtag #EndSars to rally crowds against the Special Anti-Robbery Squad (Sars).
President Muhammadu Buhari disbanded Sars on 11 October. But protests have continued, with demands for more changes in the security forces, as well as reforms to the way the country is run.
Witnesses have told the BBC what they saw when men in military camouflage opened fire on Tuesday evening.
Nigerian horror over #EndSars protest shootings
In pictures: Nigeria's End Sars protests
On Wednesday, buildings were set alight across Lagos and police put up roadblocks. A major Nigerian TV station with links to a ruling party politician was on fire after people attacked it with petrol bombs.
Police in different districts of the city fired shots in the air to disperse protesters defying the curfew, the BBC's Nduka Orjinmo reports from the capital, Abuja. He also reports that the palace of the most senior traditional leader in the city was looted, though the leader had been evacuated beforehand.
Authorities deny anybody was shot dead on Tuesday, saying that a number of people were wounded in the incident.
What happened in Lagos?
Witnesses said uniformed men opened fire on a crowd of around 1,000 demonstrators in the wealthy Lekki suburb on Tuesday.
Soldiers were seen barricading the protest site moments before the shooting, BBC Nigeria correspondent Mayeni Jones reports. Social media footage streamed live from the scene shows protesters tending to the wounded.