BANGKOK, Thailand (AP) _ A strong earthquake shook northwestern Laos and was felt in northern Thailand early Thursday, but there were no immediate reports of injury or serious damage.

The Thai government's earthquake monitoring center said the quake struck at 3:59 a.m. with a magnitude of 5.9. Its epicenter was in northern Laos, 340 miles north of Bangkok, in the Hongsa district near the border with Thailand.

In the main provincial town of Sayaboury, villagers began shooting rifles in the air after about five seconds of ``strong shaking,'' said Sisamouth, a United Nations Development Program official.

The rattling of doors and shutters from the tremor made people think intruders were trying to break into their houses, said Sisamouth, who like some Laotians uses only one name.

Across the border, the mayor of the Thai town of Thung Chang, Boonraum Sinsakulvivat, said he was woken by the shaking and told his family to run out of the house.

``We have no high buildings here,'' he said, adding that there was no damage to large storage buildings.