Protesters in Port Gentil set up barricades on main roads
Gabon will declare a "state of siege" in the city of Port Gentil if post- election violence does not subside, the interior minister has warned.
Jean-Francois Ndongou said he would seek to invoke "special powers" to ban movement if protests did not cease.
Hundreds of residents used canoes to flee the city on Sunday after three nights of clashes and three deaths.
The trouble began after the disputed poll victory of Ali Ben Bongo, son of the late former President Omar Bongo.
Port-Gentil, the country's second-largest city and an opposition stronghold, is already under a dusk-to-dawn curfew.
But despite these measures there has been widespread looting and buildings have been set on fire.
"The president and the prime minister do not want to put Port-Gentil under a state of siege," said Mr Ndongou.
"But if peace, order and harmony are not restored, we are going to solicit authorisation to do so from parliament."
Under the constitution, Gabon's president can, after cabinet discussion and consultation with parliament, decree a state of emergency or a state of siege, thus assuming "special powers under conditions set out by law".
"A state of siege is serious," said Mr Ndongou.
"There would be a ban on movement without special authorisation. Do not turn Port-Gentil into a battlefield."