For the second day in a row, there's been a mass shooting in the United States. A Seattle, Washington man walked into a building Wednesday and started firing, killing two.

Four people were shot. One died immediately, another died a few hours later while in surgery. Of those injured, one is in critical condition with a chest wound; the other is in stable condition with a gunshot wound to the arm.

The gunman escaped on foot and has not been found.

Police used tracking dogs to hunt for the gunman, who is apparently dressed in camouflage clothing. They've since given up on that idea and are expanding their search. Three schools in the area have been locked down with the children inside.

The shooting happened in a two-storey building at a shipyard in the Wallingford neighbourhood which is north of downtown Seattle.

All the victims are male and all worked at the shipping yard.

So far there's no explanation for the shooting. Witnesses say the man walked in calmly and started shooting. Witnesses did not recognize the man.

This comes a day after a disgruntled employee killed seven workers at a Xerox plant in Honolulu. He was arrested after a stand-off with police.

More details as soon as they're available.