Several protesters have been killed by security forces in Lagos in Nigeria today, Amnesty International has said.

"People were killed at the (Lekki) tollgate by security forces," said Amnesty spokesman Isa Sanusi, "we are working on verifying how many".

More than 1,000 protesters had gathered in defiance of a curfew imposed hours earlier as city officials claimed the youth-led protests that began 12 days ago had been hijacked by criminals.

The Nigerian state of Lagos had imposed the 24-hour curfew, saying recent protests against alleged police brutality had turned violent after a police station in the commercial capital was set on fire.

Thousands of Nigerians, demanding an end to alleged police brutality, have taken to the streets every day for more than a week across the country, posing a challenge to President Muhammadu Buhari.

Governor Babajide Sanwo-Olu said the curfew would affect all parts of the state, including Lagos - Africa's largest city with 20 million inhabitants. Only essential workers were exempted.

"I have watched with shock how what began as a peaceful…protest has degenerated into a monster that is threatening the wellbeing of our society," he said.

Nationwide protests have continued despite the dissolution of the Special Anti-Robbery Squad (SARS) on 11 October following accusations of human rights abuses.

A police station in the Orile Iganmu area of Lagos was set ablaze today, TV news station channels reported.

Early in the protests, police fired on protesters in the Surulere area of Lagos and elsewhere. Armed gangs have attacked protesters in Lagos and the capital Abuja.

Amnesty International said at least 15 people had been killed since the protests began, not including the people who were killed at the (Lekki) tollgate today.

The Lagos Chamber of Commerce said Nigeria's economy had suffered an estimated loss of 700 billion naira ($1.84bn) in the last 12 days due to the disruption.

Yesterday, the southern state of Edo imposed a similar curfew after a jailbreak by prisoners during protests.

The speaker of Nigeria's lower chamber of parliament, Femi Gbajabiamila, said he would not sign off on the federal budget for 2021 unless it included provisions to compensate victims of police brutality over the past two decades.

Youth minister Sunday Dare said yesterday that the government had met demonstrators' demands for talks on reforms in law enforcement and urged them to enter into dialogue.

Officials say they fear a surge in coronavirus infections due to people attending demonstrations.