A massive wildfire in the U.S. state of Oregon has grown rapidly to some 1,554 square kilometers, an area more than half the size of Rhode Island's land mass, officials said on Friday.

The Durkee Fire, sparked by lightning on July 17, is the largest blaze in the United States so far. Officials said the fire was only 20 percent contained on Friday.

Meanwhile, a single-pilot tanker plane contracted by the U.S. 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 567 square kilometers with 55 percent contained, according to the government website InciWeb.

As of Thursday, wildfires had burned almost 4,047 square kilometers in Oregon and 509 square kilometers 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 505 square kilometers on Thursday to 664 square kilometers Friday morning, according to the California Department of Forestry and Fire Protection.

More than 110 active fires covering 7,250 square kilometers were burning across the country on Friday, according to the National Interagency Fire Center.