The winner of Nigeria's presidential election in March, Muhammadu Buhari, has been sworn in as leader of Africa's most populous country.

Mr Buhari is the first opposition figure to win a presidential election in Nigeria since independence in 1960.

"I belong to everybody and I belong to nobody", he told cheering crowds at the inauguration in the capital, Abuja.

He vowed to tackle "head on" the issues of corruption and the insurgency from militant Islamist group Boko Haram.

Mr Buhari, a former military ruler, has taken over from Goodluck Jonathan, who had been in office since 2010.

At the inauguration ceremony at Abuja's Eagle Square - Mr Jonathan handed over the constitution and national flags before Mr Buhari took his oath of office.

"I will discharge my duties to the best of my ability, faithfully and in accordance with the Constitution of the Federal Republic of Nigeria and the law," he said to cheering crowds.

The announcer declared to the audience afterwards: "Change has come to Nigeria."

Among the guests at the ceremony was US Secretary of State John Kerry and African leaders including Zimbabwe's President Robert Mugabe.

Mr Buhari comes into power as Nigeria faces significant economic as well as security challenges with an Islamist insurgency having devastated towns and villages in the north-east.

Besides tackling the Boko Haram militants, Mr Buhari has promised to stamp out corruption.