Bookings for the Milford Track were effectively sold out by noon on Thursday despite the system crashing for several hours after being bombarded with requests.
The website crashed shortly after bookings opened when 10,000 people tried to book at the same time.
The system was fully restored shortly after 1pm.
Department of Conservation booking services manager Cameron Hyland said DOC acknowledged the frustration
"We acknowledge how difficult it was for some people trying to book a spot. We are now working with our IT vendor to understand the cause behind the issue we experienced and how it can be prevented from occurring again with more Great Walks bookings opening soon.
"We have had the system crash before, for example in 2021 due to high volume and limited server capacity, but in this case we had enough server capacity."
Hyland said users had been asking why bookings were shut down entirely doing the crash.
At the time, DOC encouraged users to be patient and keep trying.
"In the past we've had similar issues and they have tended to be self-resolving. Once the initial outage period passed, we were receiving high numbers of successful bookings and at that point, shutting down the system would have more negatively impacted those people.
"The Milford Track did sell out quickly despite the issues - though this was definitely a more frustrating process for the users than it should have been."
Hyland encouraged anyone who missed out to occasionally check the website as cancellations and modifications would get made in the coming weeks.
Last year, places on the Milford Track were almost completely taken up within half an hour of bookings opening.
There is space for about 7500 people to walk the track during the entire season.
Bookings for the other Great Walks will open progressively over the course of April and May and DOC said it expected interest would be high from both local and international visitors.
The Lake Waikaremoana track is closed due to flood damage, so no booking date for the upcoming season has yet been set.
Great Walks booking opening dates for 2023/24
Thursday 20 April 2023, 9.30am
Wednesday 26 April 2023, 9.30am
Abel Tasman Coast Track
Thursday 27 April 2023, 9.30am
Tongariro Northern Circuit
Tuesday 16 May 2023, 9.30am
Heaphy Track - following extreme weather damage in 2022, the Heaphy Track can be booked from either end up to 19 October, with the full track expected to be open later in the year.
Still to be confirmed
Lake Waikaremoana - is closed until at least 30 April 2023 due to flood damage. Check the Ngāi Tūhoe website for updates. The DOC website will also have alerts.