A nationwide strike is under way in Gabon where workers are calling for recent changes to the constitution to be reversed.

"We don't know exactly who is in charge of Gabon today. Let the president speak out and reassure the Gabonese people," said Louis Patrick Mombo, of trade union alliance Gabon Dynamique Unitaire.

President Ali Bongo, 59, has been out of the country since October seeking medical treatment - first in Saudi Arabia, followed by Morocco. AFP news agency reports that he had suffered a stroke.

In his absence, Gabon's Constitutional Court has amended part of the constitution to allow the vice-president, Pierre-Claver Maganga Moussavou, to hold a ministerial meetings and to unblock pending cases.

But the trade union alliance wants the president of the Senate to act as interim president, which is what the constitution specified before it was amended.