The manhunt for a US Army reservist suspected of murdering 18 people and injuring 13 others in a mass shooting in Maine has entered its second day.

Police say Robert Card is armed and dangerous and are asking people to shelter inside their homes for safety.

On Thursday night, police converged on a home in Bowdoin, around a 20 minute drive from Lewiston where the shooting happened the night earlier.

Police said they were executing several search warrants.

Loud bangs were heard at the scene, and police yelling for him to surrender.

Over a megaphone, FBI agents and local law enforcement were heard telling the suspect to come out of the house "with your hands up". But after a few hours, police departed the scene.

But it is unclear what prompted the search, and a spokesperson for the Maine Department of Public Safety said officers were "simply doing their due diligence by tracking down every lead in an effort to locate and apprehend Card".

The shooting began at a bowling alley in the small town of Lewiston just before 19:00 local time (23:00 GMT), the police colonel said. One woman and six men were killed there.

Within about 10 minutes, gunfire was reported at a nearby restaurant, Schemengees Bar & Grille, where eight more men were fatally shot.

Sixteen injured people were initially transferred to local hospitals, three of whom later died.

Meanwhile, Lewiston and three nearby towns remain under a shelter in place notice. Schools as well as most local businesses have closed and many will remain so on Friday.

Beyond a few dog walkers, most people appeared to have stayed at home on Thursday. Police are posted on the streets.

The only bustles of activity are near the two shooting sites and the Central Maine Medical Center.

Dr John Alexander, the chief medical officer there, called the attack "unprecedented" for the small city. He said about 50 medical providers, nurses, respiratory therapists and surgeons answered the call to help treat the victims.

Maine State Police said the suspect had recently reported mental health issues, including "hearing voices and threats to shoot up a military installation in southern Maine".

He had reportedly been admitted to a mental health treatment facility in the summer, after behaving erratically during training at the US Military Academy.

Police denied earlier reports that he was a firearms instructor, saying there was "no indication he attended advanced weaponry courses".

Maine's Governor Janet Mills, a former Lewiston resident, called it a "dark day" for her state and pledged "to seek full justice for the victims and their families".

The FBI and other federal US law enforcement agencies are aiding local and state police in the manhunt. Neighbouring states are also providing resources and remaining vigilant, as the suspect could have travelled across state lines.

Canadian border officials have also been warned to be on alert for the suspect.

Maine has the lowest homicide rate of any state in the US. One of the state's most famous authors, horror writer Stephen King, said the shooting occurred near his home.

"This is madness in the name of freedom," he posted on X, formally Twitter, also calling for new gun safety laws to regulate assault rifles.

In a Facebook post, Schemengees Bar & Grille wrote: "In a split second your world gets turned upside down for no good reason. We lost great people in this community. How can we make any sense of this."

Just-In-Time Recreation, where the attack first began, posted online: "None of this seems real, but unfortunately it is... There are no words to fix this or make it better."

President Joe Biden ordered flags at the White House and other federal buildings to be lowered to half-mast as a mark of respect for those who died.

He also called on Republican lawmakers in Congress to pass gun safety legislation.

"This is the very least we owe every American who will now bear the scars – physical and mental – of this latest attack," he said.

Speaking at a news conference on Thursday, Maine Senator Susan Collins called for a ban on high-capacity magazines.

"Our hearts are heavy with grief," she told reporters. "This heinous attack, which has robbed the lives of at least 18 Mainers and injured so many more is the worst mass shooting that the state of Maine has ever experienced and could ever imagine."