There was no casualty or injury, police said.
Oil India Limited said there was a leakage in an underground crude oil pipeline due to mechanical issues at the Central Tank Farm (CTF).
"The spilled crude oil somehow managed to trickle into the nearby Burhi Dihing river. It appears that some miscreants set fire to the oil floating on the river. There has been no casualty and the fire has doused on its own, an OIL statement said.
The company said: "An incident took place at the Central Tank Farm (CTF) in Oil India Limited (OIL)'s field headquarters in Duliajan. There was sudden closure of remote operated shut off valves and motor operator valves of inlets and outlets of all the Crude Oil Storage Tanks.
"Consequently, there was pressure build up in the incoming lines to the tanks and it was observed that leaks developed at five points within the periphery of the CTF. Leaks also developed at two points in the incoming crude oil delivery line of one of the field installation near Duliajan."
The authorities have formed an enquiry committee to find the root cause of the incident and suggest remedial measures.
"Normal operations have resumed and all leakages have been fixed and crude oil is being received from installations at Central Tank Farm, Duliajan," the company said.
A joint team comprising Circle Officer of Tengakhat Circle, Dibrugarh district, State Pollution Control Board, fisheries department and OIL experts were reviewing the possible damage to the environment.
Once the expert committee submits its findings, necessary action would be initiated.
The vide of the fire, with dense, huge, black smokes from the river covering the horizon, went viral on social media.
However, the officials said the damages were not of the magnitude as the video would suggest, and there were much bigger fires of such nature in the past.
However, environmental experts were concerned that the aquatic life on the river could have been damaged due to the fire.
( With inputs from IANS )