The cost to coastal states of cleaning up after a shadow tanker oil spill in South East Asia could hit $1.6bn, according to a new report.

Finland’s Centre for Research on Energy and Clean Air (Crea) said on Friday that the rise of shadow fleets, coupled with uncertainties surrounding their regulation and insurance, makes a “catastrophic” ecological event inevitable.

Shadow fleet tankers hauling sanctioned oil cargoes have been involved in at least 50 incidents, including collisions and oil spills, according to a report by insurer Allianz in May, and concerns have been raised about who will pay for a major accident.