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An investigation is underway after a shooting at a Halloween party in Ontario left an 18-year-old man dead early Saturday morning.

Officers were dispatched to the 700 block of East Bonnie Brae Court at about 12:06 a.m. after receiving reports of a shooting, the Ontario Police Department said in a news release.

After arriving, police found an unresponsive man suffering from a gunshot wound, officials said.

The young man, whose identity has not been released, was pronounced dead at the scene.

Officers found four additional shooting victims — one adult and three juveniles — who were then taken to a local hospital, the Police Department said. As of early Saturday afternoon, those victims were listed in stable but critical condition, officials said.

A preliminary investigation found that the shooting occurred during a Halloween party that had attracted an “unexpected number of guests,” police said. The majority of attendees were minors, officials added.

As of early Saturday afternoon, police did not have a suspect in custody, and no further information was immediately available.

Police are asking for the public’s help identifying those responsible for the incident. Anyone with information is asked to contact the Ontario Police Department at 909-986-6711, or Detective Kyle Mean at 909-408-1769.

Those wishing to remain anonymous can call WE-TIP at 800-78-CRIME, or go online at www.wetip.com.