A man is detained following a mass shooting in the parking lot of TOPS supermarket in Buffalo, New York. Reuters

The gunman, who was wearing body armor and a helmet, was arrested after the massacre, Buffalo Police Commissioner Joseph Gramaglia told a news conference.

READ MORE

Ukraine wages counteroffensive against Russian forces in east

G7 warn of Ukraine grain crisis ask China not to aid Russia

Gramaglia put the toll at 10 dead and three wounded. Eleven of the victims were African Americans.

The gunman shot four people in the parking lot of the Tops supermarket, three of them fatally, then went inside and continued firing, Gramaglia said.

A crowd gathers as police investigate after a shooting at a supermarket in Buffalo on Saturday. AP

Among those killed inside the store was a retired police officer working as an armed security guard.

The guard "engaged the suspect, fired multiple shots," but the gunman shot him, Gramaglia said.

He added that when police arrived, the shooter put the gun to his neck, but was talked down and surrendered.

Stephen Belongia, special agent in charge of the FBI's Buffalo field office, told the news conference that the shooting is being investigated as a hate crime.

"We are investigating this incident as both a hate crime and a case of racially motivated violent extremism," Belongia said.

Police officers secure the scene after a shooting at TOPS supermarket in Buffalo, New York, on Saturday. Reuters

Erie County Sheriff John Garcia described the attack as "pure evil."

"It was straight up racially motivated hate crime from somebody outside of our community," he said.

When asked what information led authorities to term the attack a hate crime, Erie County District Attorney John Flynn said they had evidence indicating "racial animosity," but declined to elaborate.

Agence France-Presse