In a March 19 letter to the UN, the ICS estimated that at least 100,000 seafarers a month need to change over from the ships they operate. Crews are often flown home or flown to the ports in which ships are based, and the time they spend on board a vessel depends on their rank, experience and ship type.

Most recently, India has gone on a 21-day lockdown and is enforcing a two-week quarantine on all passengers, including Indian nationals, arriving from European countries hit hard by the virus and from China. China has just banned entry to all foreign nationals.

Singapore, home to Asia’s largest container port outside China and one of the world’s top places for oceangoing cargo ships to refuel, has prohibited all visitors to enter or transit with recent travel history to France, Germany, Italy and Spain. Italy and Spain are the latest hotspots of the Covid-19 outbreak that has affected at least 700,000 people globally and claimed more than 33,000 lives.

Shipping industry in choppy waters as coronavirus evokes 2016 slump and Hanjin bankruptcy

On March 27, the Maritime and Port Authority of Singapore announced it would allow crew changes in special circumstances and with approved documentation.

Greece, home to the Port of Piraeus, one of the busiest in Europe, has prohibited crew changes and shore leave.

Some of the other issues facing shipping companies cited by ICS include delayed port clearance, prevention of crew from embarking or disembarking, prevention of loading or unloading of cargo or provisions, and in extreme cases, refusing port entry to ships.

“Limitations on crew change [the replacement of one of the ship’s crew members with another one] have the potential to cause serious disruption to the flow of trade,” said Guy Platten, secretary general of the ICS. Platten noted that Maersk, the world’s largest container cargo shipping line, has suspended all crew changes until April 14, meaning seafarers face unknown lengths of time at sea with no prospect of relief.

According to the Hong Kong Ship Owners Association, the top five national sources of crew and officers are the Philippines, China, India, Greece and Eastern Europe, including Ukraine, Poland, Russia and the Baltics.

Captain Kaushik Roy, quality and environment manager at China Energy Ship Management, which specialises in shipping LNG to China, said that delays caused by quarantines were merely headaches now, but would start hitting the bottom line eventually. He estimated that crew costs constituted at least half of the running costs of a cargo ship.

Dry bulk shipping rates remain far below levels that are profitable and container shipping rates have been supported only by the idling of nearly 10 per cent of the fleet capacity, according to BIMCO, the world’s largest shipping association.

“This is a time bomb,” said Unni, who noted that seafaring already involves crew being away from their families for long periods.

“Right now, in the midst of a pandemic when of course people are anxious, thousands are stuck at sea or stranded around the world waiting to join vessels but unable to do so.”