An 18-year-old man wearing military gear was arrested after a stand-off at the scene in the city of Buffalo. The suspect entered a busy supermarket on Saturday afternoon before opening fire. He used a camera to stream the attack online, police said.

US President Joe Biden has condemned what he called an "abhorrent" attack. "We are investigating this incident as both a hate crime and a case of racially-motivated violent extremism," Stephen Belongia, the agent in charge of the FBI's Buffalo office, told a news conference.

The suspect is believed to have driven for several hours to reach the predominantly black area of the city. Thirteen people were shot in total and the majority of the victims were black, Buffalo Police Commissioner Joseph Gramaglia said.