A three-man crew from Italy has soared more than 80 kilometres above the New Mexico desert aboard a Virgin Galactic rocket plane.

It was the company's first flight taking paying customers to the edge of space since British billionaire Richard Branson founded the venture in 2004.

Two Italian air force officers and an aerospace engineer from the National Research Council of Italy made the brief suborbital ride with three Virgin Galactic crew members.

Two of the Virgin Galactic crew members piloted the vehicle, VSS Unity, once it was launched at high altitude from the belly of its twin-fuselage carrier plane.

About 75 minutes after leaving the ground with its mothership, Unity glided back to its starting point on a runway at Spaceport America near the New Mexico town of Truth or Consequences.

Virgin Galactic leases part of the state-owned facility.

The flight marked a long-delayed breakthrough for Virgin Galactic which has been trying to commercialise flights to the edge of space for nearly 20 years.

Mr Branson founded the company with aerospace mogul Burt Rutan in a venture that grew out of the 2004 Ansari X Prize competition won by Mr Rutan's experimental spaceplane, a forerunner of the Unity.

Virgin becomes the latest commercial enterprise, along with Jeff Bezos's Blue Origin and fellow billionaire Elon Musk's SpaceX.

Commercial space flight enterprises cater to wealthy customers willing to pay large sums of money to experience supersonic rocket speed, microgravity and the spectacle of the Earth's curvature from space.

Italian science mission

The mission of the Italian team on this flight, however, was billed as a scientific one.

It involved collecting biometric data, measuring cognitive performance and recording how certain liquids and solids mix in microgravity conditions.

For Italian Air Force Colonel Walter Villadei, the flight was also part of his astronaut training for a future mission to the International Space Station.

Joining him were Lieutenant Colonel Angelo Landolfi, a physician and flight surgeon, and Pantaleone Carlucci, a research council member acting as flight engineer and payload specialist.

Rounding out the crew was their Virgin Galactic trainer, Colin Bennett, and Unity's two pilots, Michael Masucci and Nicola Pecile.

The rocket plane was borne aloft attached to the underside of its transport jet, VMS Eve.

Reaching its launch altitude roughly 14km above the ground, Unity was then released from the mothership.

As it fell away, the pilots ignited the vehicle's engine to send the rocket plane streaking in a near-vertical climb at about three times the speed of sound to the darkness of space.

Virgin Galactic said Unity topped out its flight at an altitude of nearly 85km.

At the apex of the flight, with the rocket shut down, the crew experienced a few minutes of weightlessness before the craft shifted into re-entry mode and began its descent back to Earth.

A webcast showed live footage of crew members strapped into their seats in flight suits and sunglasses as they neared the maximum height of their voyage, then enjoying the thrill of microgravity as Colonel Villadei unveiled an Italian flag in the cabin.

Space tourism on the rise

The flight came two years after Mr Branson himself rode along with five other Virgin Galactic personnel for Unity's first fully crewed test spaceflight in July 2021.

At the time, the company was targeting regular commercial service to begin in 2022 following additional test flights.

However, federal regulators grounded Unity for 11 weeks while the company was under investigation for deviating from its assigned airspace on ascent during the July 2021 flight.

A final crewed test flight to space was conducted five weeks ago.

The company had said before the launch that a successful flight would pave the way for Unity to fly again in early August, with monthly flights thereafter.

Virgin Galactic said it had already booked a backlog of 800 customers.

Most are charged between $US250,000 and $US450,000 per seat ($380,000 to $680,000).

The company aims to build a large enough fleet to accommodate 400 flights annually.

An earlier prototype of the Virgin Galactic rocket plane crashed during a test flight over California's Mojave Desert in 2014, killing one pilot and seriously injuring another.