Pol Lt Kantinant Songkhramyos, the duty officer at Muang district police station, said the fire started about 1am at New Top World supermarket, which occupied two adjoining three- and four-storey buildings with a total of 13 shop fronts at the intersection of Phosri and Surakan roads.
The first floor of the store was a supermarket with space on the second, third and fourth floors used for storing goods.
Fire engines from Udon Thani and other nearby municipalities, and from the 24th Army District and the 23rd Wing of the air force, were called out to fight the blaze.
Witnesses said the fire started on the first floor and soon spread to the upper floors. This was followed by a series of explosions. About half of the town was left without electricity for the rest of the night.
Firemen were able to bring the blaze under control about 6am. The store, which was about 20 years old, was completely gutted and all merchandise destroyed.
The damage was estimated at 100 million baht.
There were no reports of casualties. Police were investigating the cause of the fire.