Pierce County Sheriff's spokesman Ed Troyer said officers were looking for one male suspect who fled the scene and haven't ruled out an accomplice, possibly a getaway driver.
It wasn't clear whether the officers even had time to draw their weapons to return fire, Troyer said.
"This was more of an execution. Walk in with the specific mindset to shoot police officers," Troyer said.
Troyer said the officers - all from the Lakewood Police Department - were catching up on paperwork at the beginning of their shifts when they were attacked at 8:15am on Sunday (local time).
Troyer said the attack was clearly targeted at the officers, not a robbery gone bad.
"There were marked patrol cars outside and they were all in uniform," Troyer said.
With no known suspects, there was no indication of any connection with the Halloween night shooting of a Seattle police officer. The suspect in that shooting remains hospitalised.
"We won't know if it's a copycat effect or what it was until we get the case solved," Troyer said. "We don't even have a suspect ID right now."
Troyer would not release the names of the victims in Sunday's shooting, and said the motive for the shooting was unknown.
Two employees and a few other customers were in the shop during the attack. All are being interviewed by the Pierce County Sheriff's investigators.
"Some are in shock. They are very upset," Troyer said. "They are the ones who are going to put together for us how this happened."
The Forza Coffee Shop, part of a popular local chain, is on a side street near McChord Air Force Base in Tacoma, about 35 miles south of Seattle. The shop is in a small retail center alongside two restaurants, a cigar store and a nail salon.
Brad Carpenter, founder and owner of Forza Coffee, said his staff was OK and being interviewed by police, and that his main concern was with the families of the police officers.
"I'm a retired police officer, so this really hits close to home for me," he said.
Streets around the coffee shop were blocked off late Sunday morning, and a police helicopter hovered over a large crowd of investigators. TV video showed police taking possession of a pickup truck parked in a grocery store in Parkland.
"We are looking at some people. We are looking at some cars. We are looking at some residences," Troyer said.
Troyer urged people to stay away from scenes to avoid interfering and putting themselves at risks
Dave Gabrielson, a clerk at Foot Mart about a block away from the coffee shop, told the newspaper all was quiet when he opened the store at 8 a.m. About 30 minutes later, "All of a sudden a million cops were zooming up and down the road," Gabrielson said.
He said he saw officers bring a police dog into a nearby apartment complex.
The officers killed Sunday were a patrol squad made up of three officers and their sergeant. No threats had been made against them or other officers in the region, sheriff's officials said.
"We lost people we care about. We're working to find out who did this and deal with him." Pierce County Sheriff Paul Pastor told reporters at the scene.
Washington Governor Chris Gregoire said she was "shocked and horrified" by the killings.
"Our police put their lives on the line every day, and tragedies like this remind us of the risks they continually take to keep our communities safe," she said in a written statement. "My heart goes out to the family, friends and co-workers of these officers, as well as the entire law enforcement community."
At Rollies Tavern near the coffee house, the plasma TVs usually tuned to football had Northwest Cable News on. Three bar patrons live next door to the coffee house.
Jerry Arnold, 45, was in bed when he was awakened by sirens. He's lived there seven years and never seen anything close to Sunday's scene.
"I hope they get them. I can't sleep until they do," he said. "Those guys could be hiding in my backyard."
