SINGAPORE (BLOOMBERG) - Omicron is ripping through cargo ships, raising concerns that a surge in coronavirus cases, coupled with China's tightened quarantine requirements for vessels, could delay supply chain stabilisation for the shipping industry.

Covid-19 outbreaks are hitting ships globally, with cases increasing "exponentially", said Mr Francesco Gargiulo, chief executive of the International Maritime Employers' Council, which represents shipping companies.

Anglo-Eastern Univan Group, which has an active crew of about 16,000, is seeing infections on five to seven vessels a month compared with only one or two a month last year, the company said.

Meanwhile, Wilhelmsen Ship Management has had infections on four of its ships since January after less than a dozen vessels were struck with Covid-19 in all of last year, said Mr Carl Schou, chief executive at the ship manager.

"Everyone has had cases onboard," said Mr Mark O'Neil, the CEO of Columbia Shipmanagement, which operates a crew pool of about 15,000 and has seen a few of its ships struck down. "You'll probably see the number of vessels worldwide affected by Omicron increasing for sure because it's so contagious. That's despite measures and precautions being taken."

Though ship managers say the problem has been manageable so far, a sustained jump in cases adds pressure to supply chains already strained by the pandemic. Ports from Shenzhen to Los Angeles and Rotterdam are contending with long lines of cargo ships, while a shortage of workers and drivers are adding to the snarls.

The disruptions are being made worse by strict controls at ports in China, which shows no signs of backing away from its policy of trying to eradicate Covid-19 as the rest of the world resolves to live with it.

While cases are mostly mild among crew, who in most instances must be vaccinated, Omicron spreads quickly through ships. That often triggers a quarantine of the vessel for as long as two weeks, although the length of a ship's quarantine can vary from ship managers, ports and countries.

Wilhelmsen quarantines ships for two weeks in cases where infections have become widespread.

Chinese ports are especially challenging, with the authorities requiring the entire ship to be quarantined if a single seafarer tests positive. Vessels stopping in China must also have been free of Covid-19 for at least three weeks.

On top of that, crew changes in China are still near impossible for foreign seafarers. China's tightened Covid-19 quarantine requirements for vessels and reduced manpower at ports are adding to delays. It is taking a week to 10 days longer to deliver iron ore supplies into China versus before the pandemic, charterers and ship owners say.

According to data from project44, average shipment delays from China to the United States West Coast increased 114 per cent last year compared with a year earlier. The route to Europe recorded a 172 per cent surge.

"Supply chain disruption persists," said Mr Bjorn Hojgaard, Anglo-Eastern CEO and chairman of the Hong Kong Shipowners Association. "China's done a good job in preventing deaths and serious outbreaks but the reality is the international supply chain is suffering. There's no working around it."

China's zero-Covid approach could prove increasingly problematic at ports as more countries switch to living with the virus. Key seafaring countries, including India, the Philippines and parts of Europe, are being hit by big rises in infections, according to a report this month from the Neptune Declaration coalition of ship owners and charterers.

"This has caused large numbers of crew being infected, leading to postponed crew changes and increased local restrictions further complicating crew changes," it found.

Last month, about a hundred of Anglo-Eastern's seafarers tested positive right before embarkation, a jump compared with just a handful in the last quarter of last year, said Mr Hojgaard.

One bright spot: Seafarer vaccinations are rising, helping to keep symptoms mild. Many ship charters are now requiring that seafarers on vessels carrying their cargo be vaccinated, said Mr Schou at Wilhelmsen, which also requires seafarers be inoculated.

"Luckily, no crew have needed to be hospitalised and it's just influenza-like symptoms that pass in a few days," he said. "As the world opens up, we'll get much larger, much faster waves of Omicron."