Nguyen Thi Hao, 36, will be investigated for breaking regulations on fire safety and fire fighting, they said.

Hao was burning grass on a rice field near the forest in Son Trung Ward, Ha Tinh Province, and strong winds caused the fire to spread to the forest in the morning of June 27.

Hao and several other people in the area tried to put out the fire but failed.

The same day, thousands of forest rangers, firefighters, soldiers and policemen managed to extinguish the fire at 4 p.m. But more than three hectares (7.4 acres) of 30-year-old pine forest were completely burned by then. The damage is estimated at hundreds of millions of dong (VND100 million = $4,300).

Last week, police had arrested another Ha Tinh resident, a 46-year-old man, for inadvertently setting fire to 30 hectares of forest while burning trash at home. He faces the same charge as Hao.

From June 25 to 30, forest fires broke out in the communes of Nghi Xuan, Loc Da, Duc Tho, Huong Son and others in Ha Tinh Province amid recurring heat waves, turning over 250 hectares of forest to ash.