An investigation was launched following what was described as a process upset at Fife Ethylene Plant.
Elevated flaring began on Monday morning at the Mossmorran petrochemical plant, near Cowdenbeath.
Environment agency SEPA has been informed.
Plant owner ExxonMobil said it was looking into the cause of the upset.
It said: “We would like to apologise to the local communities for any inconvenience or concern we may have caused as a result of the flaring.”