Authorities are working to get to the bottom of a major cyber security breach which may have exposed the personal health data of tens of thousands of Kiwis

Health platform Manage My Health says more than 120-thousand of its users could be affected.

Chief Executive Vino Ramayah says there's information suggesting a ransom of 60-thousand-dollars is being demanded, but he can't comment, as the matter's with Police.

He says he also can't comment on who might be responsible.

Ramayah says they suspect the breach may have been carried out by someone overseas, but Police are still looking into that too.