San Francisco, Jul 27 (IANS): A massive wildfire in the US state of Oregon has grown rapidly to some 600 square miles (1,554 sq km), an area more than half the size of Rhode Island's land mass, officials have said.

The Durkee Fire, sparked by lightning on July 17, is the largest blaze in the US so far. Officials said the fire was only 20 per cent contained on Friday, Xinhua news agency reported.

Meanwhile, a single-pilot tanker plane contracted by the US Bureau of Land Management went missing Thursday while fighting another wildfire, the Falls Fire, near the town of Seneca on the edge of the Malheur National Forest.

The plane was found Friday morning, authorities said, adding that the pilot on board was killed during the crash.

The Falls Fire has grown to 219 square miles (567 sq km) with 55 per cent contained, according to the government website InciWeb.

As of Thursday, wildfires had burned almost 1 million acres (4,047 sq km) in Oregon and 125,900 acres (509 sq km) in Washington state so far this year, according to the Northwest Interagency Coordination Center in Portland, Oregon.

In California, the Park Fire has forced the evacuation of more than 4,000 residents in Butte County, north of California's capital city Sacramento. The fire grew uncontrolled overnight from 125,000 acres (505 sq km) on Thursday to 164,200 acres (664 sq km) Friday morning, according to the California Department of Forestry and Fire Protection.

More than 110 active fires covering 2,800 square miles (7,250 sq km) were burning across the country on Friday, according to the National Interagency Fire Center.