A global supertanker, the world's largest aerial firefighting aircraft, dropped fire retardant over the ongoing Glass Fire at the Robert Louis Stevenson State Park in Napa County, California.

The giant aircraft tackled the blaze, which has now consumed 66,840 acres and threatened 21,785 structures.

Fire crews said the wildfire has forced at least 68,000 residents to evacuate and is now 41 percent contained.

This year, the California wildfires have scorched more than four million acres of land and damaged 8,687 structures across the state.

A global supertanker dropped fire retardant over the ongoing Glass Fire at the Robert Louis Stevenson State Park in Napa County, California.

The aircraft was tackling the blaze that has consumed 66,840 acres and threatened 21,785 structures since it started.

Fire crews said the wildfire has forced the evacuation of at least 68,000 residents and is 41 per cent contained.

This year, the California wildfires have scorched more than four million acres of land and damaged 8,687 structures across the state.