The state-owned, Shanghai-based firm is the latest of several major shipping groups to announce suspended operations since Iran's Revolutionary Guards declared the Strait of Hormuz closed on Saturday.

"Vessels that have already entered the Gulf, after completing the operations where safe to do so, have been instructed to proceed to safe waters to hover or anchor," Cosco Shipping Lines said in a statement Sunday.

Ships headed for the Gulf "have been notified to prioritize navigational safety, with measures including speed reduction, proceeding to safe waters, or awaiting further instructions at designated sheltered anchorages", it said.

Cosco said it was "evaluating contingency plans" for all cargo on the affected vessels, "including potential alternative discharge ports", the statement added.

Other shipping giants including Maersk and MSC have also announced halted operations in the region.

State media in Oman, which sits across the strait from Iran, said Sunday an oil tanker off its coast had been targeted and four of its crew hurt.

Also on Sunday, UK authorities said that a ship off the UAE's coast near the strait reported being hit by an "unknown projectile causing a fire".