A gunman opened fire at a bowling alley and a restaurant in Maine on Wednesday, killing at least 16 people and sparking a massive police manhunt.
The shootings began early evening in the small city of Lewiston.
Police there have told residents to stay indoors, as well as in Lisbon, Bowdoin and Auburn.
They named Robert Card, 40, a firearms instructor, as a person of interest and described him as "armed and dangerous".
Police have not yet officially confirmed a death toll but CBS, the BBC's US partner, said multiple law enforcement sources said there were at least 16 casualties.
There have also been reports of at least 50 people injured.
Lewiston police said officers had responded to reports of shooting at two locations, a restaurant called Schemengees, and Sparetime Recreation, a bowling alley, which appear to be about four miles (6.5km) apart.
Riley Dumont told ABC News her 11-year-old daughter had been taking part in a children's bowling league at the bowling alley when she heard several gunshots.
She said her father, a retired police officer, had then corralled their family into a corner.
"I was laying on top of my daughter," she said. "My mother was laying on top of me."
She said that she saw three or four apparent victims.
Billie Jayne Cooke, who is running for the city council in Lewiston, told BBC News Channel she had been leaving an event as details of the shooting emerged.
"Helicopters, sirens, I've never heard so much activity in my life in this city. We have police from all over the state, from out of the state, coming up," she said.
"The whole city's on lockdown. It's horrible. You just don't think that's ever going to happen and it did."
The Androscoggin County Sheriff's Office has released images of Robert Card, asking for the public's help identifying him.
A number of images show a bearded man in a brown sweater carrying a firearm and walking into a building.
Robert Card is a firearms instructor who was trained by the US military at a facility in the city of Saco, Maine, according to a state police bulletin seen by CBS.
The bulletin also said he had spent time in a mental health centre in the summer of 2023 and had threatened to commit a shooting at the base.
The authorities also shared a photo of a white vehicle, found in Lisbon,11km (seven miles) from Lewiston, saying its front bumper was believed to be painted black, and asked anybody who recognised it to contact police.
Lewiston Public Schools Superintendent Jake Langlais said in a statement that schools in the district would be closed on Thursday.
The White House said President Biden had spoken individually by phone to Maine Governor Janet Mills, Senators Angus King and Susan Collins, and Congressman Jared Golden.
Senator King said in a statement he was "deeply sad for the city of Lewiston and all those worried about their family, friends and neighbours".
A statement from the Department of Homeland Security (DHS) said Secretary Alejandro Mayorkas had been briefed and was continuing to monitor the situation.
A US justice department statement said that federal agencies were assisting state and local law enforcement.