Northland's harbourmaster says it's lucky no lives were lost after a collision between two launches at the entrance to Whangarei Harbour.

The incident overnight - which has left both boats with significant damage - is being investigated by Maritime New Zealand.

Harbourmaster Jim Lyle says they're trying to work out why the boats didn't see each other.

"We've spoken to one of the owners. We're still trying to contact the other owner.

"It was a pretty serious collision and potentially someone could have been killed in that."