Sultan, the one-time winner of Big Brother Africa, shared two photos on his social media accounts which have more than five million followers.

One of the pictures shows Sultan posing on a presidential chair with the national seal, while the other shows Mr Magufuli's face on the comedian's body.

The caption was in Swahili, and read: "We swapped roles for a day so that he could enjoy his birthday in peace."

Shortly after the photos were posted, an Instagram comment, thought to be from Paul Makonda, the Regional Commissioner for Dar es Salaam, told Sultan to report to any police station in the city for further instructions, adding that he "doesn't know the boundaries of his work."

A relative told the BBC that Sultan had turned himself in on Wednesday evening, and had not yet returned. Sultan is being held under the 2015 Cybercrimes Act, which forbids using "computer technology" to impersonate someone else, his lawyer Eliya Rioba told the BBC.

If convicted he could face up to seven years in prison, or a fine of up to five million Tanzanian shillings ($2,170; £1,678).

The 2015 Cybercrimes Act has been criticised by human rights activists, who say it infringes on freedom of expression.

(BBC)