The Interislander ferries have been under strain during the holiday season as they coped with the loss of one ship from the fleet, a spokeswoman said.
KiwiRail communications adviser Jenni Austin said it was too early to tell how booking numbers compared to the same period last year, but they had been "very heavy".
"Ferries are full, particularly for the southward journey [to Picton]. There may be some openings for those wishing to come north," she said.
The strain on the service across Cook Strait was expected to ease from January 12, when replacement ship Stena Alegra is scheduled to begin commercial sailings.
The British-registered ship arrived in Wellington on Sunday after a month-long journey from Poland, where it had been crossing the Baltic Sea to and from Sweden. The ship made a return trip from Wellington to Picton last night.
It will act as a temporary replacement for the Aratere, which lost its starboard propeller when the shaft snapped just outside Tory Channel during a routine night sailing on November 5.
KiwiRail chief executive Jim Quinn said freight and car bookings were being accepted from January 12, but commercial sailings could be brought forward if Interislander was "concrete sure" it could be done.
Ms Austin said Interislander would spend the coming days running some trials, preparing the ship and familiarising the New Zealand crew with it.
A decision was expected within the next few days whether the ferry would be able to take foot passengers. This would be based on whether it was economically or physically viable to alter boarding gangways, but Mr Quinn said lack of foot passenger access would not be a problem, as other ships in the InterIslander fleet were able to accommodate them.
The Aratere is expected to leave Wellington for a dry dock in Asia by early February so two new propeller shafts can be fitted. No date has yet been finalised. Options include Singapore, Malaysia, the Philippines and China.
The Aratere's propeller was recovered from the bottom of Cook Strait by salvors Seaworks earlier this month. It is being examined by Transport Accident Investigation Commission investigators in a Lower Hutt workshop.
The Stena Alegra is expected to remain on the Cook Strait run for at least six months.
Ms Austin advised anyone wanting to travel with Interislander in the coming weeks to contact the booking team to see if there were any openings.
- The Marlborough Express