A wildfire is raging for a third day in the hills of northern New Mexico near the nuclear laboratory where the atomic bomb was first developed.

The blaze came within a few kilometers of a dump site where around 20,000 barrels of plutonium-contaminated waste is stored at the Los Alamos National Laboratory.

However, officials said that the fire is being kept at a safe distance and there is no danger of it reaching the low-level radioactive materials.

The Los Alamos laboratory, which was established during World War II as part of the top-secret Manhattan Project that developed the first atomic bomb, remains one of the top nuclear arms manufacturing facilities in the US.

The cause of the fire is believed to be a fallen power line.

The fire has already burned more than 25,000 hectares as its spread through the woodlands of the Sante Fe National Forest, which surrounds the lab and town of Los Alamos on three sides.  

Both the town of Los Alamos, home to about 10,000 residents, and the laboratory, with a work force of about 12,000 people, were evacuated on Monday, and the lab will remain closed at least through Wednesday, officials said.

Situated on a hilltop 55 km northwest of Santa Fe, the lab property covers 9,300 hectares and includes about 2,000 buildings, none of which has been affected by the fire.