"It is an act of sabotage, a serious terrorist act aimed at harming the interests of the nation and endangering the population," said the interior ministry.
Emergency services brought the blaze under control after it was discovered, adding that national oil company Bapco had turned off the flow of oil.
The fire service also evacuated homes in the nearby village of Buri, 15km south of Manama, it added.
Bahrain relies on the Abu Safa field, which it shares with neighbouring Saudi Arabia, for much of its oil, pumped in via a 230 000-barrel-per-day pipeline.
Bahrain, a Shi'ite-majority kingdom ruled by a Sunni dynasty, has seen sporadic violence since the repression in 2011 of a protest movement demanding a constitutional monarchy and an elected prime minister.
Authorities have since tightened their grip on dissent, jailing hundreds of protesters and stripping a string of high-profile activists and clerics of citizenship.