President John Magufuli of Tanzania, a populist leader who played down the seriousness of the coronavirus pandemic and steered his country away from democratic ideals, died on Wednesday in the port city of Dar es Salaam. He was 61.

Vice President Samia Suluhu Hassan said in a brief televised address that Mr. Magufuli had died of heart complications while being treated at Mzena Hospital. The announcement followed more than a week of intense speculation that Mr. Magufuli was critically ill with Covid-19 — reports that senior government officials had repeatedly denied.

Ms. Hassan did not specify Mr. Magufuli’s underlying illness but said that he had suffered from chronic atrial fibrillation for more than a decade. She announced 14 days of national mourning and said that flags would fly at half-staff nationwide.

According to the Tanzanian Constitution, Ms. Hassan will be sworn in as president to serve the remainder of the five-year term that Mr. Magufuli began when he won re-election last October. The move will make her Tanzania’s first female leader.