Authorities in the US state of Maine are looking for a gunman who went on a shooting rampage, killing at least 18 people and injuring 13.

The attack started Wednesday evening at a bowling alley in the city of Lewiston and, about 10 minutes later, continued at a bar a few kilometers away. Police did not find the shooter and urged people to stay indoors.

William Ross of the Maine State Police told a news conference that "the suspect should be considered armed and dangerous" and "someone that should not be approached."

Police are looking for a man who has spent years in the army reserves. They say he is a certified firearms instructor.

Researchers with the Washington-based nonprofit group Gun Violence Archive have tracked more than 550 mass shootings this year.

President Joe Biden said "far too many" Americans have had a family member killed or injured in shootings. He has urged lawmakers to work with him on gun control and ordered flags to be flown at half-staff in memory of the latest victims.