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But the demand has also caused headaches for those trying to book through the internet.
Bookings for the Routeburn Track opened on Tuesday and spaces on the Milford Track were available from yesterday morning.
Places on the Kepler and Heaphy tracks are available from today.
The Department of Conservation has increased hut fees by 30% on the Milford Track and by 20% on the Routeburn and Kepler tracks.
Heavy demand for a place on the Milford Track yesterday morning caused delays for some customers. A reader contacted the Otago Daily Times saying he could not make a booking on the website at 2pm on Tuesday.
Frustrated customers also took to social media to complain about the delays.
Department of Conservation trade marketing and sales manager Ross Shearer said there was heavy demand for both walks, which led to issues with the booking website's servers.
No issues were reported when the Routeburn Track opened on Tuesday, but very heavy demand for a place on the Milford Track caused delays.
When the Routeburn Track opened, Doc's website processed about 500 page requests per minute.
That number jumped dramatically when the Milford Track opened, to 6200 page requests per minute.
Most of the issues occurred between 10am and 11am when customers who tried to book a place were timed out, and had to access the website again, Mr Shearer said.
The issue was fixed by the afternoon.
As well as an increase in people trying to access the website, the number of bookings was up on last year.
The 1066 bookings made for a place on the Routeburn Track was a 90% increase on the same timein 2016. Bookings on the Milford Track also increased with 6071 visitors already securing a place on the walk, up from 5317 at the same point last year.