No casualty was reported in the incident, OIL sources said.
A massive operation was launched with at least 50 fire tenders from IAF, OIL, North East Electrical Power Corporation, ONGC and the state government, the sources said.
The fire broke out in oil well number 15, closed on June 15, 1992, due to high pressure and is expected to continue for the next three days, the sources said.
The blaze led to a oil spill which covered a nearby paddy field. The OIL authorities evacuated 500 families living in its vicinity.
OIL has requested the help of an expert team of fire extinguishers from Russia, who are expected to arrive at Dikom on Friday, the sources said.
The evacuees were lodged at the Dikom High School, while hundreds of labourers of the nearby Dikom tea estate were also shifted to safer places, the sources said adding OIL is providing relief materials to the evacuated.
As a precautionary measure, the district authorities have blocked NH 37 and also cut off electricity as high tension wires passed near the oil well and spillage area.