The death toll from New Zealand's devastating White Island eruption has risen to 19, with police confirming another death in hospital.

The toll includes two people whose bodies have not been recovered.

A police spokesman said they were informed that a person had died late Sunday in an Auckland hospital.

There were 47 people, mainly Australian tourists, on the island when it erupted on 9 December, and 25 remain in hospital. Many are still in a critical condition.

The sea search for the two missing people continues, although it has been scaled down.

"We haven't given up," deputy police commissioner Mike Clement said after telling the families why they believed the bodies were not on the island.

"But we are literally in the hands of the sea... the reality is we cannot be precise.

"I think the family understands as time passes it means less chance but not, no chance."