Hailstones, sometimes the size of large limes, started falling about 30 minutes after heavy rain on Sunday around 2pm. It was the most severe hailstorm in Loei province in decades, according to reports.
Wanchai Chaiwiset, head of the provincial meteorological station, said strong winds and low temperatures in cumulonimbus clouds caused rain droplets to freeze and then fall as hailstones. They ranged in size from 50 millimetres across to 100 millimetres - the largest ever seen in Phu Rua.
The hailstones gathered in deep icy drifts, like snow drifts.
Mr Wanchai said hail typically occurs during summer storms, but these hailstones were exceptionally large.
Phu Rua district chief Boonterm Renumas said more than 500 homes in eight villages were damaged by the hail storm.
Mr Boonterm said village chiefs and other local officials had been instructed to provide prompt help to people and to quickly clear roads and assess the damage.
Sirimarn Sriburin, a manager at Chachanat Woodland in Phu Rua, said the storm caused a power cut that lasted several hours. Temperatures on the ground plummeted to about 14 degrees Celsius, he said.