Thousands of residents calmly fled from the New Mexico town that is home to the Los Alamos nuclear laboratory, ahead of an approaching wildfire that sent up towering plumes of smoke, rained down ash and sparked a spot fire on lab property where scientists 50 years ago conducted underground tests of radioactive explosives.

The US government's Los Alamos National Laboratory declared an emergency today after a fast-moving wildfire forced officials to close the nuclear site in New Mexico.