Two people have been killed in a shooting at a Colorado Christian missionary center.

ARVADA, Colo. - A gunman walked into a training center dormitory for young Christian missionaries early Sunday and opened fire, killing two of the center’s staff members and wounding two others. No arrests had been made by late morning.

The shooting happened at about 12:30 a.m. at the Youth With a Mission center, police spokeswoman Susan Medina said. About 45 people were evacuated from the dormitory in this Denver suburb.

A man and a woman in their mid-20s died, and two men ages 22 and 23 were wounded, Medina said. One of the injured men was in critical condition, said Paul Filidis, a Colorado Springs-based spokesman with Youth With a Mission. All four of the victims were staff members, Filidis said.

Witnesses told police that the gunman was a 20-year-old white male, wearing a dark jacket and skull cap. He may have glasses or a beard.