Officials in the northwestern US state of Washington have expressed concern over reports of people organising "Covid-19 parties" to intentionally spread the virus.

"Gathering in groups in the midst of this pandemic can be incredibly dangerous and puts people at increased risk for hospitalisation and even death," warned John Wiesman, the state's secretary of health.

Wiesman's comments came after officials in Walla Walla County, located 420 kilometres southeast of Seattle, reported that some of the nearly 100 cases in the region appear to have been intentionally spread or contracted at so-called "Covid-19 parties."

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