Los Angeles, June 30 (IANS/EFE) A wildfire that has scorched more than 28,000 hectares near the Los Alamos nuclear laboratory in New Mexico continued to rage out of control Wednesday, although authorities played down the risk of a radioactive smoke plume.

The blaze has increased in size by 12 percent over the past day and may now have charred more than 40,000 hectares despite efforts by 1,000 firefighters backed by the National Guard.

Only one spot fire has been detected thus far in the vicinity of the nuclear installations and it was extinguished rapidly, lab operators said.

Preliminary results from several Environmental Protection Agency air-quality tests in the zone affected by the fire, which began Sunday, showed no presence of radioactive particles.

The Los Alamos National Laboratory is a centre for classified research on nuclear weapons and the place where the first atomic bomb was developed.

Lab officials said Wednesday there is no present threat to radioactive material stored at the facility or to the 10,000 drums of plutonium-contaminated radioactive waste housed in the complex's Area G, which is more exposed to the elements.

The city of Los Alamos, home to 12,000 residents, was evacuated Monday due to concerns the fire may affect the urban area.