Liberia's new President Joseph Boakai has been declared "perfectly fine" by his doctors, his office says.

The 79-year-old failed to reach the end of his inauguration speech and had to be helped away from the podium during his swearing-in ceremony on Monday.

His office said he had suffered heat exhaustion but had now resumed his normal activities.

Concern about Mr Boakai's health was a major issue during last year's election campaign.

He narrowly defeated the outgoing president, 57-year-old former football star George Weah, in a run-off election in November.

Mr Boakai had been speaking for around 30 minutes at his inauguration when it became clear that he was having difficulty continuing.

He had already been sworn in as Liberia's oldest-ever president at the outside ceremony held at the Capitol Building, the seat of parliament in the capital, Monrovia.

The temperature had reached more than 30C in swelteringly humid conditions.

Video footage from the ceremony had shown a man fanning papers near Mr Boakai's face, before he was taken away.

"His doctors have declared him perfectly fine," Charles Snetter from the president's office said in a statement.

An official in Mr Boakai's party told the AFP agency that the president was not taken to hospital.

"The president is normal, and he's doing well," Amos Tweh said.

Before he was forced to cut short his speech the new president pledged to rescue all Liberians from the tough economic times, address corruption and improve basic services.

Mr Boakai was vice-president in Nobel Peace Prize-winner Ellen Johnson Sirleaf's government until 2018, and contested the presidency under the banner of the United Party (UP).

He defeated Mr Weah by just over 20,000 votes in the run-off vote.

Mr Boakai also ran for the presidency in 2017, but lost to Mr Weah, who became Liberia's young-ever elected president.