The condition of the MV Wakashio was worsening early on Saturday and it split by the afternoon, the Mauritius National Crisis Committee said.
"At around 4.30pm, a major detachment of the vessel's forward section was observed," it said in a statement. "On the basis of the experts' advice, the towing plan is being implemented."
The vessel struck a coral reef on July 25, spilling about 1,000 tonnes of fuel oil and endangering corals, fish and other marine life in what some scientists have called the country's worst ecological disaster.
On Friday, some residual oil from the ship leaked into the ocean, Mauritius Marine Conservation Society President Jacqueline Sauzier told Reuters on Saturday morning.
Authorities deployed booms on Saturday to help with oil absorption around the vessel.