Mauritius was bracing Monday for tropical cyclone Belal, with the authorities warning of possible flooding as the storm "dangerously" approaches the Indian Ocean island nation after hitting the French overseas territory of Reunion.

The Mauritius Meteorological Services said in a statement that a cyclone warning level three (out of four) was in force and advised the public to stay in a safe place, with "torrential rain conditions" expected in the coming hours.

It said the cyclone was about 170 kilometres (105 miles) west of Le Morne, which lies on the southwest of the island, and was moving east-southeast at a speed of about 12 kilometres an hour.

"On this trajectory, Belal is dangerously approaching Mauritius and it represents a threat for Mauritius," the meteorological office said.

"The radius of cyclonic winds is likely to cross the southern part of the island and Belal is expected to pass closer to the south of the island early tomorrow (Tuesday) morning.

"Heavy rainfall will cause water accumulations and flooding in several places," it added, warning of a storm surge and inundation along low-lying areas near the coastline.

The Bank of Mauritius said it would be shutting its branches due to "the deteriorating weather conditions".

Airports of Mauritius said Sunday that the country's main international airport would "maintain its operations, as far as possible, for a maximum of 3 hours after the issue of a Cyclone Warning Class 3."