The MV XpressPearl is currently sinking after taking on water since yesterday, the Marine Environment Protection Authority has said.
A resultant oil leak could spread as far as Dikowita and Negombo, they have warned.
The ship was due to be towed out to deep waters today.
There have been two explosions on board the 2,700 twenty-foot equivalent unit-capacity container ship since it initially caught fire on May 21 at anchor near the Sri Lankan port of Colombo. The fire, which had appeared to have taken hold on most of the vessel as of May 26, continued to burn for a few days.