Lewiston police have identified a person of interest as Robert Card.

Police in Maine have identified a person of interest in the shooting, according to multiple law enforcement sources.

The person of interest has a history of military service and is a firearms instructor, the sources said.

The sources said he also has a mental health history, including a two-week stay this summer at a mental health facility after he allegedly made threats about carrying out a shooting at a National Guard facility.

Authorities have traced his white Subaru to a location in Lisbon, Maine, sources said.

The Lewiston Police Department has issued a shelter-in-place order for the city. Residents are urged to stay inside with their doors locked.

The FBI is sending in aviation units to help in the search for the gunman. New Hampshire police are putting up roadblocks to try to confine the gunman if he’s on the run.

Maine Gov. Janet Mills said in a statement, "I am aware of and have been briefed on the active shooter situation in Lewiston. I urge all people in the area to follow the direction of State and local enforcement."

New Hampshire Gov. Chris Sununu said New Hampshire "officials have been in touch with our counterparts in Maine to offer and provide any medical and safety resources needed as they manage this horrific situation. Our hearts and prayers are with the people of Maine."

President Joe Biden spoke on the phone with Gov. Mills, Maine Sens. Angus King and Susan Collins and Rep. Jared Golden, D-Maine, and "offered full federal support in the wake of this horrific attack," according to the White House.

Lewiston Mayor Carl Sheline said in a statement, "I am heartbroken for our city and our people. Lewiston is known for our strength and grit and we will need both in the days to come."

Lewiston is about 35 miles north of Portland, Maine.

A nurse at Maine Medical told ABC News the shooting unfolded at a bowling alley during its youth night.

"Maine Medical is on lockdown right now awaiting Lewiston patients," the nurse said. "They just called for [emergency department] nurses and critical care nurses to come in [and] set up three stretchers to each single critical care bay. They just got their first two patients -- both gunshot wounds to their thighs."

At least 16 people are believed to be dead, though that number is in flux, and dozens more have been injured after a bowling alley came under fire in Lewiston, Maine, Wednesday evening -- the deadliest shooting of the year and one of the deadliest in recent decades.

Riley Dumont said she heard a loud bang after which her father, a retired cop, corralled them into a corner and put protection in front of them including "tables and a big bench that the kids were hiding behind."

“I was laying on top of my daughter. My mother was laying on top of me,” said Dumont. "It felt like it lasted a lifetime," she added. "I just remember people sobbing and crying."

Another witness at the bowling alley, whose name is Brandon, but whose last name was not made available, described hearing a "loud pop."

"Thought it was a balloon," Brandon said. "I had my back turned to the door. As soon as I turned and saw that it was not a balloon, he was holding a weapon. I just bucked it down the lane and I slid basically into where the pins are and climbed up to the machine and was on top of the machines for about 10 minutes until the cops got there."

Meghan Hutchinson, another shooting witness, said, "We were very scared and we didn't know, like, we didn't know what to do, what to expect from this. You know, nothing like this has ever happened here before. We barricaded in there and another parent was in the room with me. She had a phone and she called 911."

Zoe Levesque, 10, was grazed by a bullet.

“I never thought I'd grow up and get a bullet in my leg," said Levesque. "Like, why do people do this? I was more worried about, like, am I going to live and going to make it out of here? Like, what's going to happen? Are the cops going to come?"