Authorities in Spokane County in the US state of Washington said on Monday night that they had arrested a 37-year-old man suspected of starting one of three wildfires burning in and around Spokane.

As of Monday, about 64,000 people had been ordered to evacuate the area, with at least 700 structures destroyed and another 400 damaged. The fires have burned more than 4,000 hectares.

The causes of the other two blazes remain under investigation.