The family of Tanzanian billionaire Mohammed Dewji, who was kidnapped on Thursday, has offered a 1bn Tanzania shilling ($440,000; £330,000) reward for information that leads to his rescue.

Mr Dewji, reportedly Africa's youngest billionaire, was taken by masked gunmen in the Tanzanian city of Dar es Salaam.

The police have arrested more than 20 people in connection with the abduction

But both the motive for the kidnapping and his whereabouts are still unclear.

Police believe that two white men were behind Mr Dewji's disappearance, reports the BBC's Athuman Mtulya from Dar es Salaam.

The family hoped that the reward will help the police's investigation, spokesperson Azim Dewji told a packed press conference.

"We want to assure anyone with the information about the whereabouts of our son to come forward and we will treat their information as secret," he said.

Kidnappings are uncommon in Tanzania, our correspondent says.(BBC)