OAKLAND, California - A gunman walked into a Tacoma, Washington-area, coffee shop on Sunday morning and fatally shot four police officers, law enforcement officials said.

The four were preparing for their day shift shortly after 8 a.m. when the man shot them with a handgun, they said.

Pierce County Sheriff's Department spokesman Ed Troyer described the shootings at the Forza Coffee shop as an ambush.

"There were baristas in there and other customers and they were not hit," said State Trooper Brandy Kessler.

Troopers and other law enforcement officials are helping with the investigation in the Tacoma suburb of about 60,000, which is about 40 miles southwest of Seattle and near McChord Air Force Base.

The gunman escaped and a US$10,000 reward for information has been offered, Troyer said.