NYINGCHI, Tibet, April 20 (Xinhua) -- More than 6,700 fire-fighters and local residents are still struggling to control a fire spreading through virgin forest in Tibet Autonomous Region, said local sources on Friday.

    Yulha, vice commissioner of the Nyingchi prefecture administrative office, said they were recruiting more people to help control the blaze which is continuing to spread.

    Thick smoke was spotted at about 5:10 p.m. on Thursday in a forest four kilometers from the Bayi township, in the Nyingchi Prefecture, southeast Tibet.

    Strong winds fanned the fire and by 6:00 a.m. Friday, the fire had moved more than five square kilometers, Yulha said.

    Fire-fighters have dug 10-kilometer-long firebreaks on the east and west sides to prevent the blaze from reaching local hospitals, schools, villages and the No. 318 national highway, Yulha said.

    But the fire is still spreading south, he said, adding that they have also started to dig firebreaks in the southern area.

    Yulha said the local fire-fighting headquarters had ordered creation of artificial rain in an effort to quench the fire. He said two oil tanks, which are about 700 meters away from the blazing forest, are so far safe from the blaze.

    No casualties have been reported.

    Hu Chuyang, a senior engineer with the Tibet observatory, said rain was forecast over the weekend. "It can't extinguish the fire, but would be helpful in curbing the fire spread," he said.

    Two fires broke out in eastern Tibet in March, destroying about three million square meters of forest.