The oil spilled after two ships, the MT BW Maple, carrying liquefied petroleum gas and the MT Dawm Kanchioyram, an oil tanker, collided at the Kamarajar Port (Ennore) anchorage on Saturday.
The Port authorities in their Press Note on Saturday said, "There is no damage to the environment like oil pollution and no casualty or injury to persons."
But according to local reports, the dark sludge appears to have reached beaches as far as 25km away from Ennore.
Quoting Tamil Nadu Fisheries Minister D Jayakumar on Tuesday, Chennai Online reported that about one tonne oil has spilled into the sea following Saturday's collision and it is expected to take ten days to clear the oil spill.
The Coast Guard's Pollution Response Force - along with pollution control bard, fire and rescue officials - have launched a mopping operation using submersible pumps, reported NDTV.
The oil slick has already affected the local environment and the livelihood of the people. Fishermen in and around Ennore are not able to go fishing due to the sludge, media reported.