At least eight of those victims were underground when the waters began to rise rapidly Saturday, the BBC said. Six bodies were recovered from a pedestrian subway and two others were found in an underground parking lot.
A seventh victim died of a heart attack during the flood, the BBC said.
Meteorologists said 6 inches of rain fell in less than an hour Saturday. Residents were advised to stay home Sunday, as more rain was expected.
Prime Minister Navin Rangoolam, in a nationally broadcast address, declared Monday a day of mourning.
He said Mauritius is suffering from the effects of climate change.