Nevada has called on three of the top firefighting crews in the nation to help fight its wildfires, among the most voracious in the U.S.

A national command team and the three crews joined the battle Thursday against Nevada fires that have blackened 240,000 acres, or nearly 375 square miles, of rangeland and threatened ranches, mines and wildlife habitat.

Nevada's fires are among the nation's largest. Wildfires have scorched more than 1 million acres nationally, or 1,563 square miles — slightly more land mass than the state of Rhode Island.

A fire in Lander County in central Nevada has exploded to 130,000-pl us acres, or about 203 square miles, and was 20 percent contained. Despite threats of thunderstorms and high humidity Thursday, firefighters were optimistic.

While Nevada got assistance with its blazes, other states are worried there won't be enough help as summer ends. In just the past week, more than 100 requests for a 20-person fire crew went unfilled in Washington and Oregon alone, said Kathy Fletcher, spokeswoman for the Northwest Interagency Coordination Center in Portland, Ore.

The center estimates state and federal agencies, as well as contract fire crews, will lose 15 percent of their firefighters as they return to college and other jobs in the next few weeks.

"The extended forecast indicates no relief," Fletcher said. "The good news is the days are getting shorter and the nights are getting cooler, which helps in the firefighting efforts."

Nine large fires were burning Thursday in both Washington and Oregon.

In Montana, firefighters battling a wildfire that has charred more than 195,000 acres, or 304 square miles, had planned to work through the night Thursday to take advantage of cooler weather. They hoped to allow residents who evacuated 265 homes return to their homes on Friday.

Officials were trying to keep the fire from spreading farther west into the Boulder River Valley, dotted with numerous historic ranches and vacation homes. The movie "The Horse Whisperer" was filmed there.

The blaze, sparked by lightning on Aug. 22, was 50 percent contained on Thursday.

Lightning sparked three more fires in Idaho Thursday, bringing the total number of large blazes burning in the state to 17, the most in the nation.

In California, a fire in the Los Padres National Forest has spread rapidly after erupting Monday afternoon just northwest of Castaic. It grew from 4,200 to 7,000 acres, or nearly 11 square miles, between Wednesday and Thursday.

The fire was approaching a part of Ventura County's water supply Friday and was expected to burn through canyons and oil fields as it raged out of control for a fifth day.