Oil tankers and cargo vessels anchored off Port Sultan Qaboos in Oman. Getty ImagesOil tankers and cargo vessels anchored off Port Sultan Qaboos in Oman. Getty ImagesHapag-Lloyd says vessels 'ready for transit' – but focus remains on safety of crews

Ship transits through the Strait of Hormuz halved to 17 on Sunday from 35 after Iran’s Revolutionary Guard declared the waterway closed.

Several vessels sailed dark by switching off tracking transponders, obscuring routes and cargo movements in both directions.

Tehran previously agreed with the US to keep the strait open, prompting a brief rebound to 25 crossings and plans by Kuwait and Iraq to raise output.

Traffic remains far below pre-war levels of at least 100 daily crossings since hostilities between the US and Iran began on February 28.