The state of Washington, in the North-west of the United States, is battling its largest wildfire on record.

The flames have devoured more than 1,000 square kilometers of land so far, burning over 200 homes and now threatening thousands more.

Heavy smoke has grounded firefighting airplanes and helicopters, making it difficult to contain the flames.

At Okanogan county, near the Canadian border, Incident commander Todd Pechota said firefighters were gradually making progress against the fires.

2015 US wildfires
2015 US wildfires

"The only way to deal with them is like eating an elephant, one bite at a time. And there's still a lot to eat," Pechota said.

Three firefighters were killed and four injured last week while trying to contain the flames.

The weather is expected to remain hot and windy this week in the Pacific Northwest, heightening the risk of more blazes to come.

Dozens of wildfires are currently roaring across parts of the west of the United States, including in California, Oregon and Idaho.

Firefighters from Australia and New Zealand have volunteered to help the 32,000 US crews already in the field.