The refinery in Shuaiba, 80 kilometres (50 miles) south of Kuwait City, was shut down after the fire broke out in its heavy oil unit. It is not expected to resume full operations for a week, Kuwait National Petroleum Company (KNPC) spokesman Mohammed al-Ajmi told AFP.
The blaze was extinguished some three hours after it started without causing any casualties, he said.
"A fire started after a small explosion in the heavy oil unit about 1:00 p.m. local time (1000 GMT). That led to a total shutdown of the refinery," Ajmi said.
"The refinery was evacuated of all its employees as a safety precaution while fire-fighters began their work to put out the fire," he said.
Ajmi said state-owned KNPC has formed a team to investigate the blast and assess the damage. The losses initially appeared to be limited, he said.
In remarks to the official KUNA news agency, Ajmi ruled out sabotage as a cause of the blast. "There was no act of sabotage behind the explosion... which resulted from a crack in the gas line" feeding the heavy oil unit, he said.
Ajmi told AFP that refinery officials needed two days to isolate the unit affected by the blaze, after which operations are expected to resume gradually and the refinery will be fully operational again after a week.
Shuaiba is one of three KNPC refineries, which together with Al-Ahmadi and Mina Abdullah have a combined production capacity of 920,000 bpd.
OPEC member Kuwait sits on about 10 percent of the world's oil reserves and currently pumps some 2.5 million bpd. The Gulf emirate exports 2.2 million bpd of crude, some 40 percent of which is in refined products.
Ajmi said that exports of oil products "will not be affected at all" by the shutdown of the Shuaiba facility, as the shortfall can be compensated from storage tanks.
He said exports would be unaffected despite the fact that some units at Mina Abdullah refinery, which has a capacity of 250,000 bpd, are also currently closed for maintenance.
The Shuaiba fire was the latest incident to plague Kuwait's oil industry in recent years.
In June 2000, an explosion caused by a gas leak at Al-Ahmadi -- the country's largest refinery -- killed seven people and injured 50, and two technicians were killed and four injured by a gas leak at Shuaiba.

Copyright AFP (Agence France-Presse), 2006