A Liberian ship with the capacity to carry at least 30 passengers sank off the port of Harper 700 kilometres south of the capital early yesterday, the port manager said.
"We do not know yet how many persons have perished in this incident because the rescue team is still working," the manager, Patrick Dunor, told AFP.
Officials said they had no information on survivors or on what had caused the Liberian-owned M/V Hevea to sink.
"M/V Hevea was heading to my port when it sank. It is difficult now to say how many people died and how many survived but the passengers were travelling from Monrovia to Harper," Mr Dunor added.
Harper has Liberia's third-largest sea port and is the provincial capital of Maryland county, situated less than seven kilometres from neighbouring Ivory Coast.
Liberians travel between the two points by sea in the rainy season from May to September due to the often impassable condition of dirt roads in the country.