Liberia's new president, Joseph Boakai, has recovered from an episode of heat-induced faintness that caused him to cut short his inauguration speech on Monday before being led off the podium, his party's spokesman said.

The 79-year-old, who defeated George Weah in a runoff election in November, was sworn in during an outdoor ceremony in sweltering heat in the West African nation's capital, Monrovia.

Boakai then paused during his speech and aides rushed to fan him. He resumed a few minutes later but halted again and aides helped him walk away from the podium, curtailing the ceremony.

"It is the heat. The heat was high. They should have had some fan or something around there," Mohammed Ali, the spokesman for Boakai's ruling Unity Party said after the incident.

"At his age, the exhaustion happened. But it is okay now," he said at the event.

Some of Boakai's opponents had raised concerns about his age and energy during election campaigning but his team dismissed the criticism.

Although the inauguration ceremony ended abruptly, Boakai had already taken the oath of office when he was helped away. Officials still proceeded to a planned lunch but Boakai's whereabouts were not immediately clear.