On Sunday afternoon Interisland announced they have received dispensation from Maritime NZ for two sailings to go ahead on Sunday night if no additional crew test positive for Covid-19.

About 55 Interisland ferry staff have Covid-19 or are isolating as close contacts, initially forcing the cancellation of today's Cook Strait crossings.

Maritime NZ have now allowed two sailings to go ahead if the stipulated criteria are met. These are 8pm Wellington to Picton, with latest check in 7pm, and 12.40am Picton to Wellington, with latest check in 11.40 pm.

About 900 passengers were booked to travel between Picton and Wellington, but sailings were cancelled earlier on Sunday because there were not enough specialist staff to crew them.

"We cancelled several passenger sailings today due to multiple crew members testing positive for Covid-19. The health and safety of our passengers and crew is our top priority," says an Interisland spokesperson.

"We hope to confirm these sailings following an additional round of testing. We will open any available spaces for booking on the website once we have confirmed our ability to safely sail. You will be able to login to our website and reschedule existing bookings at that time.

"We are offering full refunds, on all fare types, if you would prefer to travel at another time.

"We recommend you can cancel bookings by logging into our website, or filling out the online refund form because our contact centre is currently experiencing very heavy call volumes.

A guide to cancelling travel is available through the website.

Earlier: 2pm:

Earlier on Sunday Interisland announced that 'under maritime law we are unable to carry passengers without a minimum contingent of crew.

"We have been moving crew between our ships to keep our services operating but this isn't possible today," says a KiwiRail spokesperson.

'Our team is working hard to keep our ships sailing as Omicron continues its spread throughout the community. We know any disruption to travel is an inconvenience.

'But given uncertainties of when staff will be cleared to work again and the possibility of further positive Covid-19 test results in our team, we are unable to rebook [passengers] onto another sailing in the near future,” the company says.

'We are processing refunds today or you can go to the website and cancel your sailing yourself. If you are booked to travel with us this week or through to the end of March, we are offering full refunds, for all fare types. You can cancel your travel by logging into the website or by calling 0800 802 802, 8am-5pm Monday to Sunday.

'If you have paid for your Interislander travel by credit card you can cancel online regardless of the fare type you booked. If you have paid by direct debit you will need to ring 0800 802 802 or fill out the online refund form.”

Passenger services were cancelled today, but the ferries would still able to sail carrying freight.

The company had been reorganising crew rosters between ships to keep services operating, but even then wasn't able to meet the crew requirements for the Kaitaki because of the number of staff off sick.

The company requires all passengers to show proof they're fully vaccinated, or a negative Covid-19 test from within 72 hours of their trip.

A Bluebridge spokeswoman said while some of their staff also have the virus the company hasn't had to cancel any sailings and Bluebridge passenger sailings are continuing as scheduled.