At least 10 people were killed and three more wounded Saturday after a gunman opened fire in a Buffalo, N.Y., supermarket in a mass shooting law-enforcement officials said they are investigating as a racially motivated hate crime.

Buffalo Police Commissioner Joseph Gramaglia said the suspect, an 18-year-old white male, drove to the Tops Friendly Markets store from out of town. He was heavily armed and wearing tactical gear and a helmet, Mr. Gramaglia said at a news conference.

The suspected shooter is from Conklin, N.Y., a suburb of Binghamton about 3½ hours southeast of Buffalo, according to a law-enforcement official briefed on the investigation. The suspect appeared before a judge Saturday and was arraigned on murder charges, the Associated Press reported.

The suspect first shot four people in the parking lot, three of whom have died, according to Mr. Gramaglia.

Inside the store, the gunman encountered a retired Buffalo police officer who worked at the store as a security guard. The two exchanged fire and the security guard died, Mr. Gramaglia said.