Four more people have died in a coronavirus outbreak in Washington state, bringing the total fatalities there to six.These are the only deaths due to Covid-19 on US soil. The northwestern state declared a state of emergency over the weekend.Five of the deaths occurred in King County, where Seattle is the main city.There are now 18 confirmed cases in the region, where there are growing fears it may spread further.Researchers who studied the first two Washington deaths had said the virus may have been spreading there for weeks, and suggested that up to 1,500 people may have been infected.Kathy Lofy, Washington state's health officer, said cases were confined to two counties - King and Snohomish - but that it was possible it was spreading elsewhere.She said the virus was "actively" spreading in those two counties.King County is to buy a hotel so it can isolate the growing number of patients in the region. More schools in the Seattle closed from Monday as cases increased.Dr Jeff Duchin, the chief health officer for Seattle and King County Public Health Agency, said there would be no widespread school closures at this stage, nor would major events be cancelled. But, he said, the number of cases is expected to increase."We are taking this situation extremely seriously," he said.Elsewhere in the US on Monday:

• New York Governor Andrew Cuomo said the state's first case was a 39-year-old female health care worker who had been in Iran before returning to the US last week
• The woman did not take public transportation and is not believed to have been contagious either on the plane or in the car returning home. Her spouse, also a healthcare worker, is being tested
• Officials in Florida said a man in his 60s and a woman in her 20s who had returned from northern Italy had tested positive

The first of the US cases were announced on 21 January.