Washington officials are preparing quarantine sites in anticipation of more coronavirus patients in the Seattle metropolitan area.

On Wednesday, Washington Governor Jay Inslee toured a small section of the Maple Lane School, where recreational vehicles are being prepared for people to test who test positive for COVID-19.

"The vast majority of people actually have a positive virus aren't going to need medical attention. And that's the folks who are going to be here in this situation," Inslee said after stepping out of one of eight RVs that are being prepared to quarantine and isolate patients.

"The smaller minority, and I've heard estimates, again, these are estimates, 20 per cent of folks who might need medical attention, those are going to be in different locations than these facilities," he added.

Four of the RVs will be used to isolate patients, while the other four will be used to quarantine them, according to the Department of Health.

King County is preparing its quarantine facilities. The county purchased 18 modular units that are in the process of being moved on to a strip of land east of Seattle.

Also in the works is the purchase of an Econo Lodge Motel near Seattle, for which the county is paying $4 million. The motel contains 85 beds and was identified as a preferable site since each room has its separate door and HVAC unit.

With these facilities combined, county and state officials will be able to quarantine at least 100 coronavirus patients. Of the 39 people who have tested positive for coronavirus in Washington, all are either at home or in hospital, according to the county's public health department.