The number of travellers flying between Australia and New Zealand has climbed since the quarantine-free bubble opening in April.

Data from Stats NZ shows there were 85,900 border crossings in April 2021, made up of 47,000 arrivals and 38,900 departures.

These numbers were well up on the monthly average of 26,300 that crossed the border in the months preceding the travel bubble.

"Despite this increase, arrivals and departures are significantly lower than levels before COVID-19, when border crossings were as high as 1.2 million in April," population indicators manager Tehseen Islam said.

"Provisional data for May 2021 show further increases in border crossings."

Trans-Tasman travel made up about 80 per cent of all international travel in April.

Provisional border crossing data up to 6 June 2021 also showed a small increase in travel with the Cook Islands each week since two-way quarantine-free travel opened on 17 May 2021. However, this is well below levels in the same period in 2019.

Since the opening of the two-way bubble a month ago, most traffic has been from Australia with many passengers being expat Kiwis wanting to reunite with family and friends.

Even before the bubble opened demand was not as high as airlines - Air NZ, Qantas and Jetstar - had predicted.

"Since the two-way trans-Tasman bubble opened last month, bookings have generally been stronger out of Australia than New Zealand. We're seeing that Kiwis need a bit of encouragement,'' said a Qantas spokesperson said earlier this month.

"We're confident that as we enter the winter months, the warmer climate of Queensland will lure more travellers from New Zealand to visit places like the Gold Coast and Cairns for a holiday."

While demand has been sluggish out of New Zealand, Queenstown is proving a big drawcard for Australians.

On all routes to Queenstown flights are operating at more than 170 per cent of pre-Covid levels and Qantas has dropped fares to stimulate demand. Route analyst firm OAG database showed the three airlines operating 455 flights into the system for the week of April 19.

They quickly took out 148 flights within a week of operation, demonstrating what OAG was uncertainty in the market and the lack of consumer confidence.

The subdued demand has led Virgin Australia to delay a return to most of its network across the Tasman until next year. The airline, which pre-Covid had 18 per cent of the market, will run some ski season and summer flights into Queenstown but main centre routes are on hold.

In 2019 there were 6.4 million passengers who flew between Australia and New Zealand, according to OAG Traffic Analyser.

Passenger flight numbers out of Auckland to Australian destinations are running at an average of 12 a day - a sharp increase on a lockdown low last year of just one a day at times.