A Managed Isolation and Quarantine (MIQ) spokeswoman said the website went live at 8am and 7500 returnees had registered by 1.30pm. The department was pleased with the fast uptake of the new system, she said.
The heavy online traffic meant some people were unable to access the booking system for nearly an hour.
Despite an initial assurance that travellers could book up to three months ahead, that was not possible today. Most travellers were only able to book up until the end of November. That caused significant stress for people trying to get home before Christmas.
The spokeswoman said flight data was only being loaded on the website once MIQ was confident about their reliability.
"Due to the international upheaval to air travel caused by Covid-19, flight data a few months out can be very changeable," she said.
Flight details for December and January would be updated by the end of the day, the spokeswoman said. MIQ apologised to travellers for the inconvenience.
Expats expressed their frustration on social media, saying that they were unable to log in to the website or that they could not book beyond November.
"This is very stressful," one person said. "It is almost midnight where I am and have spent four hours trying to seek clarity on the situation."
Another person said they had changed their flights out of concern that there would be no space in managed isolation in December.
Travellers can reserve a spot in managed isolation for 48 hours while they book their flights.
Since New Zealand went into lockdown in late March, 56,764 people have been through managed isolation facilities.