Both sides accused each other of firing first in clashes about 150 km (93 miles) southwest of Preah Vihear temple, which is claimed by both Southeast Asian nations and saw an armed stand-off in February.
"There was gunfire coming from Cambodia's side," Yutthana Viriyakitti, deputy governor of the northeastern Thai province of Surin, told Reuters, adding that authorities were evacuating hundreds of villagers from the area.
Pich Sokhin, provincial governor of Cambodia's Oddar Meanchey province, said clashes erupted at around 6:30 a.m. (7:30 p.m. EST Thursday) in areas around the Ta Moan and Ta Krabei temples. "The fighting is still going on and the Thais fired at us first," Pich Sokhin said.
A hospital in Panom Dongrak, a district in Surin province, said six Thai soldiers had been hospitalized with injuries but there were no details on the seriousness of their condition.
An international court awarded the temple to Cambodia 49 years ago but both countries lay claim to a 4.6 sq km (1.8 sq mile) patch of land near it.
The temple, known as Preah Vihear in Cambodia and Khao Phra Viharn in Thailand, sits on land that forms a natural border and has been a source of tension for generations.
They have been locked in a standoff since July 2008, when Preah Vihear was granted UNESCO World Heritage status, which Thailand opposed on grounds that the land around the temple had never been demarcated.
At least three Thais and eight Cambodians were killed and dozens of people wounded in heavy fighting over February 4-7. Sporadic clashes have broken out since then.
Thailand and Cambodia agreed on February 22 to allow civilian and unarmed military observers from Indonesia to be posted along their border. But the arrangement -- brokered by a meeting of Association for South East Asian Nations (ASEAN) foreign ministers -- has yet to be put in place.