DAR ES SALAAM-- The man said to be Africa's youngest billionaire has been kidnapped by masked gunmen in Tanzania's main city Dar es Salaam, police say.

Mohammed Dewji, 43, was abducted outside a hotel gym in the affluent neighbourhood of Oysterbay where he was going for his routine morning workout.

Three people have been arrested in connection with the incident and two of the abductors were believed to be foreign nationals, police added.

The kidnappers fired shots in the air before driving away with the billionaire, eyewitnesses said.

Dewji, a fitness enthusiast, had no security guards with him and had driven to the gym on his own, Dar es Salaam regional police commissioner Paul Makonda told reporters.

Two of the kidnappers were white men, he added.

Security personnel across Tanzania have been put on high alert in the hunt for the abductors, police said.

The motive for Dewji's abduction is still unclear.

Financial magazine Forbes puts his wealth at $1.5bn, and has described him as Tanzania's only billionaire. In a 2017 report, it said Dewji was Africa's youngest billionaire.

Dewji is also a major sponsor of one of Tanzania's biggest football teams, Simba.

Dewji, locally known as Mo, is credited with turning his family business from a wholesale and retail enterprise into a pan-African conglomerate. His company, MeTL, has interests in textile manufacturing, flour milling, beverages and edible oils in at least six African states.

Dewji served as a ruling party MP for a decade until 2015.