Heavily armed police surrounded a home on Thursday as they searched for a US Army reservist who authorities say killed 18 people and wounded 13 in a mass shooting in Lewiston, Maine.

“You need to come outside now with nothing in your hands. Your hands in the air,” police shouted through a megaphone outside the home owned by suspect Robert Card’s relative near the town of Bowdoin.

Dozens of law enforcement officials had descended on the property, with extended announcements calling for Card and anyone in the home to come out into the driveway.

In most instances when police execute warrants — even for suspects wanted for violent crimes — they move quickly to enter the home.

“The announcements that are being heard over a loudspeaker are standard search warrant announcements when executing a warrant to ensure the safety of all involved,” state police spokesperson Shannon Moss said.

“It is unknown whether Robert Card is in any of the homes law enforcement will search.”

Officials later left the property, saying they were there to execute a search warrant.

Hundreds of law enforcement agents, including dozens of FBI agents, have been hunting for Card, a 40-year-old reservist with a history of mental health issues, since Wednesday night’s shootings at a bowling alley and a bar.

Schools, doctor’s offices and grocery stores closed and people stayed behind locked doors in cities as far away as 50 miles from the scenes of Wednesday night’s shootings in Lewiston.

Superintendent Jake Langlais said Lewiston Public Schools will be closed again on Friday, writing in a post on the district’s website: “We remain in a shelter in place situation.

“We will not open buildings or run bus transportation.”

President Joe Biden ordered all US flags to be flown at half-staff as condolences poured in from around the nation and at home, including from author and Maine native Stephen King, who called it “madness”.

The attacks stunned a state of only 1.3 million people that has one of the country’s lowest homicide rates: 29 killings in all of 2022.

Card is considered armed and dangerous and should not be approached, authorities said at a news conference.

Card underwent a mental health evaluation in mid-July after he began acting erratically while with his reserve regiment, a US official told The Associated Press.

Earlier, police had not said if they have seen Card since the shootings at Schemengees Bar and Grille and at Just-In-Time Recreation, a bowling alley about four miles away.

The Androscoggin County sheriff’s office released two photos of the suspect walking into the bowling alley with a rifle raised to his shoulder.

Investigators also have not said what weapon or weapons Card used in the shootings or how he obtained them.

Maine Governor Janet Mills promised to do whatever was needed to find Card and to “hold whoever is responsible for this atrocity accountable… and to seek full justice for the victims and their families”.

Eight murder warrants were issued for Card after authorities identified eight of the victims, police said.

Ten more will likely be issued once the names of the rest of the dead are confirmed, said Maine state police colonel William Ross.

Three of the 13 people wounded in the shootings were in critical condition and five were hospitalised but stable, Central Maine medical centre officials said.

The attack started at Just-In-Time Recreation, where a children’s bowling league was taking place, just before 7pm on Wednesday.

One bowler, who identified himself only as Brandon, said he heard about 10 shots, thinking the first was a balloon popping.

“I had my back turned to the door. And as soon as I turned and saw it was not a balloon — he was holding a weapon — I just booked it,” he told the AP.

He said he scrambled down the length of the alley, sliding into the pin area and climbing up to hide in the machinery.

Less than 15 minutes after the shooting began, numerous 911 calls started coming in from Schemengees, which was offering 25% discounts to customers who work in the bar or restaurant industry.