Athletes start to race at 2020 Los Angeles Marathon in Los Angeles, the United States, March 8, 2020. (Xinhua/Qian Weizhong)

Jay Inslee, governor of the US state of Washington, announced a ban on gatherings and events of more than 250 people in King, Snohomish and Pierce counties on Wednesday at a news conference in an effort to contain the coronavirus outbreak.

The restriction, which covers gatherings for social, recreational, spiritual, sports and other events to slow the spread of COVID-19, is in effect through March and "very likely" could be extended beyond this month and could be expanded in the coming days, Inslee said.

"This is a virus... at least 10 times more potentially fatal than the flu, and this demands a response consistent with the nature of the threat," Inslee said, adding the coronavirus outbreak has been declared a pandemic by the World Health Organization.

The state has to get ahead of the curve to reduce the interaction of people in daily life, the governor said. "This is an unprecedented public health situation and we can't wait until we're in the middle of it to slow it down."

Inslee also asked school districts to make contingency plans for possible closures and suggested the workplaces should maximize telecommuting options for as many employees as possible.

The state's latest number of COVID-19 cases is 269 and statewide coronavirus death total is 25.