US police have searched in forests, waterways and small towns for an Army reservist who they say killed 18 people and wounded 13 in a mass shooting at a bowling alley and a bar in Maine.

Schools, doctors’ surgeries and shops closed and people stayed behind locked doors in cities as far as 50 miles from the scenes of Wednesday night’s shootings in Lewiston.

President Joe Biden ordered all US flags to be flown at half-mast as condolences poured in from around the nation and nearby, including from Maine native and author 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.

The suspect, Robert 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 during training, a US official told The Associated Press.

Police said they have had no reported sightings of Card since the shootings at Schemengees Bar and Grille and at Sparetime 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.

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”.

“We are not, and we will not, rest in this endeavour,” she said.

Eight murder warrants were issued for Card, 40, after authorities identified eight of the victims. Ten more will likely be issued once the names of the rest of the dead are confirmed, said Maine State Police spokesman William Ross.

Three of the 13 people wounded in the shootings were in a critical condition and five were in hospital but stable, Central Maine Medical Centre officials said.

The attack started at Sparetime, 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.

Brandon 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.

Patrick Poulin was supposed to be at the bowling centre with his 15-year-old son, who is in a league that was practising on Wednesday.

They stayed at home but he estimates there were probably several dozen young bowlers, aged 4 to 18, along with their parents, in the facility. Mr Poulin said his brother was there and shepherded some of the children outside when the shooting began.

“He’s pretty shook up,” Mr Poulin said on Thursday. “And it’s just sinking in today, like, wow, I was very close to being there. And a lot of the people that got hurt, I know.”

April Stevens lives in the same neighborhood where one of the shootings took place. She turned on all her lights overnight and locked her doors. She knew someone killed at the bar and another person injured who needed surgery.

“I’m still working because I can work from home. My husband cancelled his jobs today to stay home with me. We’re praying for everyone,” Ms Stevens said through tears.

Authorities launched a multi-state search for Card on land and water. The Coast Guard sent out a patrol boat on Thursday morning along the Kennebec River but after hours of searching, they found “nothing out of the ordinary”, said Chief Petty Officer Ryan Smith, who is in charge of the Coast Guard’s Boothbay Harbour Station.

Card’s car had been discovered by a boat launch near the Androscoggin River, which connects to the Kennebec, and Card’s 15ft boat remains unaccounted for, Mr Smith said.

Several FBI agents and other heavily armed officers gathered on Thursday afternoon off a road where several relatives of Card lived near Bowdoin. A military-style vehicle and a white van arrived and someone repeatedly yelled: “FBI! Open the door!”

The Canada Border Services Agency issued an “armed and dangerous” alert to its officers stationed along the Canada-US border.

A US official said Card was training with the Army Reserve’s 3rd Battalion, 304th Infantry Regiment in West Point, New York, when commanders became concerned about him.

State police took Card to the Keller Army Community Hospital at West Point for evaluation, according to the official.

Immediately after the shooting, police armed with rifles took positions around Lewiston, Maine’s second largest city, with a population of 37,000. The once overwhelmingly white community has become one of the most diverse cities in northern New England after a major influx of immigrants, mostly from Somalia, in recent years.

Schools 50 miles away in the town of Kennebunk closed as the search continued. Maine’s largest city, Portland, closed its public buildings.

Art teacher Miia Zellner was one of the few people out. She came with friends to central Lewiston, where they hammered about 100 paper hearts into trees with the words “To My Neighbours.”

“This is just my way of showing my love and my support for the community,” she said. “I just hope that people, when they see this, get some type of positivity from it and feel some sense of hope.”