The Latvian-registered Sava Lake had contacted Dover Coastguard on Friday night to report an incident on board.
A spokesman for Kent Fire and Rescue said the deaths, which are not being treated as suspicious, were believed to have been caused by a chemical leak.
The vessel, which was carrying ferrous metal from Denmark to Portugal, moored at Dover Harbour at 2150 GMT.
The ship with a seven-strong crew on board had alerted Dover Coastguard at 1905 GMT after the deceased, believed to be either Latvian or Russian, were discovered.
'Non-hazardous cargo'
A spokesman for Kent Fire and Rescue said: "A specialist chemical response team was sent to identify any dangerous atmospheres on board."
Kent Police added that the ship's cargo was non-hazardous, and posed "no risk to the public".
A spokeswoman said the force was conducting a joint investigation on behalf of the coroner with the Marine Accident Investigation Branch.
Gwyn Prosser, the Labour MP for Dover who spent more than 20 years at sea, praised the coastguard and the emergency services for their prompt response.
But he said seafaring was still a very dangerous occupation with people going into confined spaces which had very little ventilation being one of the most common forms of death.
"Whatever the outcome of this inquiry, I'm sure that lessons will be learnt that might make life a little bit safer for seafarers in the future," he said.
Further From BBC:
Checks follow cargo ship concerns Firefighters have been making regular checks on a container ship in Dover where two crew members were found dead, following concerns about its cargo.
The Latvian-registered Sava Lake moored in Dover on Friday after the deaths were discovered. They were thought to have been caused by a chemical leak.
Kent Fire and Rescue Service said it was keeping an eye on the temperature of ferrous metal on board.
Maritime and Coastguard Agency officers detected a heat presence at 1435 GMT.
A spokeswoman for Kent Fire and Rescue Sevice said officers had continued to make periodic checks on the temperature of the Sava Lake's cargo to make sure the ship was safe to sail.
The vessel is expected to leave the Port of Dover on Tuesday.
Kent Police said the ship's cargo was non-hazardous, and posed "no risk".
The ship with a seven-strong crew on board had alerted Dover Coastguard at 1905 GMT on Friday after the deceased, believed to be either Latvian or Russian, were discovered.
Kent Police are conducting a joint investigation on behalf of the coroner with the Marine Accident Investigation Branch.
Story from BBC NEWS:http://news.bbc.co.uk/go/pr/fr/-/2/hi/uk_news/england/kent/7201574.stmPublished: 2008/01/21 22:54:39 GMT