Soldiers opened fire on Nigerian protesters in the Lekki district of the commercial capital Lagos on Tuesday, shooting at least two people, three witnesses told Reuters.
Protesters have demonstrated for more than a week over allegations of police brutality in Nigeria.
"They started firing ammunition toward the crowd. They were firing into the crowd," said Alfred Ononugbo, 55, a security officer. "I saw the bullet hit one or two persons," he said.
Lagos state government said it would open an investigation into the shooting, which witnesses said took place around 7 p.m. local time.
"There have been reports of shooting at the Lekki Toll Plaza," Gboyega Akosile, a spokesperson for the governor, said on Twitter. "The State Government has ordered an investigation into the incident," he said in another tweet.
A Nigerian army spokesperson did not immediately respond to requests for comment.
Inyene Akpan, 26, a photographer, said more than 20 soldiers arrived at the toll gate in Lekki and opened fire. He said he saw two people being shot.
Akinbosola Ogunsanya, a third witness, said he saw around 10 people being shot. He also said he saw soldiers remove bodies.
A Reuters witness heard sirens and gunfire.
Authorities on Tuesday imposed a round-the-clock curfew on Lagos, which contains Africa's biggest city, in response to the protests, which the state governor said had turned violent.
The national police chief also ordered the immediate deployment of anti-riot forces nationwide following increased attacks on police facilities, a police spokesperson said.
Amnesty calls reports 'credible'
Amnesty International said late Tuesday there was "credible but disturbing evidence" that security forces had fatally shot protesters in Lagos.
The Lagos state commissioner for information, Gbenga Omotoso, said in a statement Tuesday night only that "there have been reports of shooting at the Lekki Toll Plaza following the 24-hour curfew imposed on Lagos."
"The state government has ordered an investigation into the incident," he said.
Video shown on Nigeria's Channels Television appeared to capture audio of live rounds being fired at the scene.