Denver police say four people were set on fire during an attack at a home in the northwest part of the city.

Police spokesman Sonny Jackson says two men showed up at the front door at about 7:30 p.m. Thursday. Some words were exchanged, and a woman who answered the door was sprayed with a flammable liquid from a pump bug sprayer and set afire. Three other adults in the home also were sprayed with flammable liquid and set afire.

The woman suffered serious injuries and was transported to a hospital, while the other three suffered minor injuries.

Jackson says the matter is under investigation and a motive had not yet been determined.

The Denver Post reports the suspects were still at large.