An investigation is getting underway, into yesterday's fatal helicopter crash near Kaikoura

Two people died in the crash at the Kekerengu river mouth, and three children are seriously injured.

Aviation commentator Irene King says if the helicopter was part of a commercial operation, the Transport Accident Investigation Commission will take the lead on the investigation.

But she says if it doesn't fit their criteria, the Civil Aviation Authority will be responsible.

She says the investigation will be thorough and comprehensive, because of the fatalities.