Nigeria is increasing restrictions for workers in its offshore sector after six offshore support vessel crew tested positive for coronavirus.
The seafarers are on board the 93-loa support ship Siem Marlin (built 2009) off Lagos.
The Nigerian Ports Authority (NPA) said the crew were tested last week by the Nigeria Centre for Disease Control.
Health officials accessed the vessel by helicopter.
Non-essential staff currently at offshore/remote locations should be withdrawn with immediate effect.
Sarki Auwalu
Vessel journey
According to Reuters ship tracking, the vessel left the Onne Port Complex on the Bonny River Estuary on 15 March, and in February visited the offshore terminals for Bonga and Bonny Light crude oil, two of Nigeria's primary export grades.
The vessel is operated by Marine Platforms of Lagos.
As a result of the positive tests, Nigeria's petroleum regulator has ordered oil and gas companies to reduce their offshore workforce and move to 28-day staff rotations.
Authorities are concerned about the potential for a widespread outbreak in Africa's most populous country, which so far has 97 confirmed cases and one death from Covid-19.
The country is keen to protect oil production, which provides 90% of much-needed foreign exchange.
It does not want the disease spreading to rigs.
Sarki Auwalu, director of the Department of Petroleum Resources, said only staff on essential duties would be allowed to travel to offshore or remote locations.
"Non-essential staff currently at offshore/remote locations should be withdrawn with immediate effect," he said in a statement.
