Around 50,000 people are expected to check the Warbirds Over Wanaka airshow this Easter weekend.

A wide range of international war planes and modern aircraft have been flown south especially for the event, and the planes weren't only in the skies.

The Catalina Flying Boat was the star of a special amphibious aircraft display along the town's waterfront as part of the biennial airshow.

"You're lowering a 12-tonne speedboat essentially that's doing over 80 mp/h onto the lake," says Catalina Pilot Brett Emeny.

"And you have to have it just at a nice altitude so it touches down and skims along."

Mr Emeny and a team of volunteers have spent 15,000 hours and hundreds-of thousands-of-dollars restoring the plane.

They see it as an aviation heritage project, with the unique World War Two plane having great significance to New Zealand.

"We operated 50 Catalinas up in the Pacific. So there were just hundreds of New Zealanders involved in either flight crew, air-gunners, navigators," says Mr Emeny.

"And even special people like Sir Edmund Hillary spent his wartime in a Catalina as a navigator."

Down the road at the Warbirds over Wanaka airshow itself, it was practice day for pilots and their planes.

Hercules, flown by the Royal New Zealand Airforce, is one of a number of operational machines sharing the airfield with classic warplanes.

A record four Air Forces are flying at the airshow -- with crews from the United States, Australia and France joining the Royal New Zealand Airforce in the skies.

But the Hercules was dwarfed by the C17 Globemaster from the US Airforce.

The plane can fly 24-hour non-stop missions using air to air refuelling, but it was too heavy to land at Wanaka Airport.

"It's a massive aircraft. Not quite as big as a C5 but still fairly large. It's about 56 metres wide, about 56 metres long, and approximately five stories tall," says US Airforce captain Logan Smith.

Wanaka is also hosting a team from NASA, who are back in town preparing to launch a second super pressure balloon from the airport.

A test launch last March saw the stadium-sized balloon fly for just over a month at high-altitude.

It's hoped improvements made to the technology will help triple its flight time.

And this time the balloon will be carrying a payload weighing over a thousand kilograms.

"Our instrument is an X-ray telescope, and we're going to be surveying the southern sky, this is where the galactic centre is, says US Berkeley Physics Chairperson Professor Steven Boggs.

"And we are looking at the sky in very high energy x-rays instead of optical light like we see with our eyes."

Newshub.