Firefighters in North China's Inner Mongolia Autonomous Region have contained the southern and western borders of a forest fire that broke out on Wednesday night, police said on Friday.

More than 1,500 firefighters have begun cleaning up the scene and searching for more flames, officials said.

"Our men are surrounding and extinguishing visible open fires around the clock," a police officer at the battlefront headquarters said. He declined to be named, but added that no casualties have been reported.

"We will beef up our forces to launch a general attack and put out all of the open fires at night if strong wind power trails off by then," the officer said.

Lightning strikes over the Gaojishan mountain area located in the Wunu'er Township of Yakeshi, a county-level city in Hulunbuir city were blamed for starting the fire, local sources said.

Force 5 to 6 winds, with gusts of up to force 8, helped the fire spread through a large area covered by dry grass, left over by persistent local droughts. The height of the grass was as high as 60 centimetres, and other items in the fire's path were highly combustible, sources said.

In recent days, at least eight areas of the forest, with an estimated area of 15 square kilometres, burst into flames, making the situation severe, officials said.

However, the task of tackling the flames was very difficult because of strong winds during the day, they said. Only when winds abated after 7 pm on Friday did officials decide to take serious action to stamp out the fire.

Local sources said the Gaojishan mountain area has a very complicated topography, which adds to the difficulty to containment efforts.