The MV Wakashio ran aground on a coral reef on 25 July with 4,000 tonnes of the fuel, causing an ecological emergency.
Most of the fuel had already been pumped out, officials said, but on Saturday the ship’s condition worsened.
Mauritius is home to world-renowned coral reefs, and popular with tourists.
The MV Wakashio ran aground at Pointe d’Esny, a known sanctuary for rare wildlife. The area also contains wetlands designated as a site of international importance by the Ramsar convention on wetlands.
“At around 4.30pm [12:30 GMT], a major detachment of the vessel’s forward section was observed,” the Mauritius National Crisis Committee said in a statement on Saturday.
Source: BBC