The night sky above the Aoraki National Park and Mackenzie Basin in Canterbury has been declared an International Dark Sky Reserve - one of only four in the world.

"To put it simply, it is one of the best star-gazing sites on Earth," executive director Bob Parks said.

More than 4300sq km of sky in the South Island is now protected as a reserve. That makes it the largest in the world.

The skies are almost completely free from light pollution.

Outdoor lighting controls were put into place in the area in the early 1980s, which helped to minimise light pollution around the Mt John Observatory, which overlooks the Tekapo township.

Christchurch and Canterbury Tourism chief executive Tim Hunter said it was fantastic news for Canterbury and was expected to bring stargazers from around the world.

"It's wonderful finally to have recognition in both national and global terms for this premium asset," Mr Hunter said.

"It puts the Mackenzie Basin on the map as a destination of international significance and sends a clear message to people that if they want the ultimate dark-sky experience, then this is the place to come."

He expected a significant increase in visitors to the Mackenzie Basin as a result of the designation.

There are 17 International Dark Sky Places worldwide, but only four International Dark Sky Reserves.

The other three are at Mont Megantic in Canada, Exmoor National Park in Britain and the NamibRand Nature Reserve in Namibia.

Mackenzie Tourism general manager Phil Brownie said Mt John was considered one of the most accessible observatories in the world.

"The observatory is home to six telescopes, including the country's biggest telescope, which measures 1.8m across and can observe 50 million stars each clear night."APNZ

- APNZ