Emmerson Mnangagwa was officially sworn in as president of Zimbabwe on Sunday after winning a bitterly-contested election which was the country's first since the ousting of strongman Robert Mugabe.

Mnangagwa, whose victory in the July 30 polls was challenged by the main opposition, pledged to "protect and promote the rights of Zimbabweans" at an inauguration ceremony attended by thousands of supporters at a stadium in Harare.

"I Emmerson Dambudzo Mnangagwa swear that as president of the republic of Zimbabwe I will be faithful to Zimbabwe (and) will obey uphold and defend the constitution of Zimbabwe," he said to thunderous applause from a crowd that also included several African heads of state.

"We must now focus on addressing the economic challenges facing our nation," he said. "We are all Zimbabweans, what unites us is greater than what could ever divide us.

Since independence from Britain in 1980, Zimbabwe has known only two presidents - Mugabe, who ruled with an iron fist for 37 years, and his erstwhile right-hand man Mnangagwa.

Nicknamed "The Crocodile", Mnangagwa was appointed after Mugabe was forced out by the military in November last year.