An intense police search continued for the suspect, who fled on foot and was still at large late on Wednesday, police said.

The four men were shot in the Northlake Shipyard office in Seattle's shipyard district by an unidentified man believed to be wielding a nine-mm semi-automatic pistol.

"He walked in and started shooting," said police spokeswoman Pam McCammon. "That's all we know."

One victim died at the scene, while a second died later at Harborview Medical Center, officials said.

The shooter was described as 1.80 metres (five ft, 11 inches) tall, a white man or light complexioned black man with a "scraggly" beard or moustache, police said.

A woman who works in an office across the hallway from where the shootings occurred said she saw a man in his 30s walkcalmly into the building at around 10.32 a.m. (1830 GMT on Wednesday).

The Seattle shooting is the latest in a string of multiple shootings in the United States this year, including a mass murder carried out by two high school students in Littleton, Colorado in April.

Wednesday's shooting followed the rampage on Tuesday in Honolulu, Hawaii, when a disgruntled employee opened fire at a Xerox building and killed seven people.

In Washington, President Bill Clinton voiced "shock and profound sorrow" over the two most recent shootings.

"I don't think we understand fully just how much more violent the United States is than other countries," the President said during an address in the White House's Rose Garden.