Supporters of Gabon opposition candidate Jean Ping have set the national assembly on fire after President Ali Bongo was declared winner of Saturday’s presidential election.
Police were using tear gas and water cannon to try to quell street protests.
Mr Bongo secured a second seven-year term with 49.8% of the vote to Mr Ping’s 48.2 %, a margin of 5,594 votes.
Mr Ping disputes the result. His camp has said figures from the president’s stronghold showed a 99% turnout.
In 2009, Mr Bongo took over from his father, who came to power in 1967.
Before entering politics Mr Ping was a renowned career diplomat.
‘Thousands of people, including young people are taking part in the protest.
Witnesses said flames and smoke could be seen rising from the national assembly building in Gabon’s capital, Libreville.
Security forces fired tear gas to disperse supporters of Mr Ping who were also trying to access the electoral commission (Cenap) headquarters.
Blanche Simonny, a Jean Ping supporter and member of the civil society group Ca Suffit Comme Ca (Enough is Enough), told BBC Focus on Africa that thousands of people had gathered at the opposition headquarters before starting the march to the commission.
She said smoke was billowing from burnt tyres left on the streets.
Mr Ping supporters were chanting ” Ali must go”.
There was no independent statement from Cenap, after Interior Minister Pacome Moubelet-Boubeya announced the results.
Delegates representing the opposition on the commission walked out of the vote count and refused to sign papers validating Mr. Bongo’s victory, according to a BBC Afrique reporter in Libreville.
Before entering politics Mr Ping was a renowned career diplomat who served as the chairman of the African Union Commission.