BANGKOK, May 6 -- Monday's earthquake in northern Thailand was the strongest tremor originated from an epicenter within this country so far.

Suchatvee Suvansavat, head of the Engineering Institute of Thailand, announced on Tuesday that the 6.3-magnitude earthquake with a seven-kilometer-deep epicenter in Phan district of the Thai northernmost province of Chiang Rai was the country's strongest tremor.

The tremor, which occurred at 6:08 p.m. local time and covered a 30-kilometer radius on the surface of the earth, was caused by the so-called Phayao Fault, south of Chiang Rai province, he said.

The Phayao Fault last caused a 5.2-magnitude tremor in 1994, according to Vorasarn Abhaipong, deputy chief of the Department of Mineral Resources.

The authorities have warned local villagers of those northern provinces such as Chiang Rai, Phayao and Lampang to stay away from high structures or those under construction as more than 100 aftershocks have occurred since.

Landslides might possibly occur due to the repetitive aftershocks in the northern provinces, according to Suchatvee.

The authorities were prompted to declare a 72-hour alert in those northern provinces as current rainfalls were feared to worsen the situation.

"Aftershocks of the tremor from the Phayao Fault might possibly recur from May 5 until May 7, given heavy downpours and the areas within a 50-kilometer-radius of the epicenter should be put on alert for possible damages," he said.

The aftershocks have occurred in the areas around the Phayao Fault's epicenter several times per hour in Chiang Rai and Phayao since Monday evening but no serious damage was reported so far.

However, one two-story brick house under construction in Chiang Rai's Mae Saruay district completely caved in due to the tremor.

Meanwhile, acting Culture Minister Sonthaya Kunpluem assigned the authorities to assess damages caused by the tremor to Buddhist stupas and temples in the affected areas including those built by reputed national artist Chalermchai Kositpipat at Chiang Rai's Rong Khun temple.

Some of the northern stupas were reported to have been partly damaged by the tremor.

Acting transport minister Chatchart Sitthipun inspected a major road between Chiang Mai and Chiang Rai which had a one-kilometer- long cleavage caused by the earthquake and told highway officials to make a detour for motorists.

The caretaker government under acting premier Yingluck Shinawatra approved 500 million baht (about 16 million U.S. dollars) in contingency funding for repairs and maintenance of property and infrastructures dented by the tremor.