The Commerce Commission is investigating possible anti-competitive behaviour between two state-funded weather forecasters, who essentially do the same job.

Private weather forecaster WeatherWatch has been asking for open access to data and complaining for some years that National Institute of Water and Atmospheric Research (Niwa) and MetService's pricing had been too restrictive.

A spokesman for the commission says it had opened an investigation under the Commerce Act.

WeatherWatch chief executive Philip Duncan claims Niwa and MetService picked "winners and losers with as a way for them to powerfully limit competition in the private sector".

WeatherWatch complained about MetService to the commission in September last year, claiming the state-owned enterprise's delays in releasing publicly available weather information from surface and upper-air observations were affecting its business.

Delays of up to six hours in making it available on the MetService website meant it lost most of its usefulness for forecasting.

But Philip's claim this breached the Fair Trading Act was squashed by the competition watchdog.

MetService says it did not yet have any detailed information about the investigation, but it would "fully co-operate with all investigations led by the Commerce Commission on this matter".

Niwa says it welcomed the investigation but would not comment while the inquiry is under way.

A Stuff investigation into how New Zealand has ended up with two state-owned forecasting companies has discovered official approval was never given to Niwa, which focuses more on climate, to develop a weather forecasting service.

Instead, Niwa made its own decision and, in a 2015 briefing for former National Party minister of science and innovation Steven Joyce, was quoted as saying it was "comfortable with the overlap with the MetService and regards the situation as manageable at the moment".

A report the Ministry of Business, Innovation and Employment released in January last year into public access to both MetService and Niwa weather data their restrictions on data were far tougher than in the United States, Norway, Australia, the United Kingdom and France.

It says the two players could potentially be stopping third-party competition and holding back innovation.

Philip says New Zealand's weather sector was behind the rest of the developed world "for no other reason than commercial greed within Government circles".

"We want our Government forecasters to do better as well and for that to happen we all need a fair and even playing field, transparency and honesty - like all other first world nations."