Sierra Leone was holding 11 Guineans including military personnel in custody on Wednesday following a confrontation at sea involving the two West African neighbours' navies, Sierra Leonean officials said.
The incident occurred early on Monday morning off the coast of northern Sierra Leone near the countries' border, the officials said.
Vessels from the two countries exchanged gunfire after Guinean naval forces illegally boarded a Chinese fishing vessel in Sierra Leonean waters, said Al Shek Kamara, Head of Operations for the Sierra Leone Police.
He said the Guineans had been holding the vessel's crew at gunpoint demanding money.
Guinea rejected that version of events.
"There was a Chinese boat that was being pursued by the Guinean navy and entered into Sierra Leone's territory. During the manoeuvre, the Guinean navy entered into Sierra Leone's territory," said government spokesman Damantang Albert Camara.
He said the Guinean personnel had disembarked to carry out administrative formalities and would return home soon.
"There was no gunfire or arrests," Camara said.
West Africa, home to some of the world's richest fishing waters, loses up to $1.5 billion worth of fish each year to vessels fishing in protected zones or without proper equipment or licenses.
Under-equipped West African maritime forces are struggling to clamp down on illegal foreign vessels, many of them Chinese.
One fifth of China's distant water fishing fleet now operates in Africa, Greenpeace said in a report published last year. Beijing rejected the accusation.
(Reporting by Umaru Fofana; Additional reporting by Saliou Samb in Conakry; Writing by Joe Bavier; editing by John Stonestreet)