Rescue workers retrieved a 10th corpse from the sea, according to journalists at the scene, as Prime Minister Said Fofana went to the site of the disaster.
A local security source had earlier said that nine people were dead and around 30 others unaccounted for after the boat collided with another vessel soon after leaving port yesterday.
"It slammed straight into a mining ship... And sank," the source said.
The mining ship belonged to the Forecariah Guinea Mining company, a joint venture set up by Australia's Bellzone and the China International Fund (CIF) to mine iron ore, he added.
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"It capsized at sea not far from (the market town of) Benty, leaving nine dead while 18 escaped," said a statement read on television earlier.
The accident happened off Forecariah province, already badly hit by the deadly Ebola virus which has spread in Guinea and neighboring Liberia and Sierra Leone.
Maritime accidents occur frequently off the 300-kilometer Guinean coast.
In August 2012, one incident left 30 dead not far from the capital Conakry.