The officers, three men and a woman, were wearing bullet proof vests and did not even have time to return fire as the killer, armed with a handgun, unleashed a volley of shots and then fled.

The attack immediately raised fears of a repeat of the massacre at Fort Hood military base in Texas, where Major Nidal Hasan killed 13 people on Nov 5.

The gunman burst into the Forza coffee shop, which is on a side street next to the base in Tacoma, Washington, 40 miles south of Seattle.

The victims were working on laptops preparing paperwork ahead of their shifts when the gunman attacked at 8.15 am.

Police said the officers were deliberately targeted and the attack was not a robbery that went wrong.

"This was more of an execution. Walk in with the specific mindset to shoot police officers," said Ed Troyer, the Pierce County Sheriff’s spokesman.