Police are concerned for the welfare of a father and daughter who are travelling by catamaran to the Bay of Islands from Kawhia Harbour in the Waikato.

Alan Langdon, 49, and his daughter Que Langdon, 6, left Kawhia Harbour on Saturday, December 17, for the Bay of Islands but their family have had no contact with them since they left.

'Police have grave concerns for their wellbeing and are seeking information from other boaties who may have seen them over the past few days.

The boat is described as a catamaran, 6 metres (21ft) in length and sail ID number T878.

The catamaran is white with blue anti-fouling paint under the waterline.

If you have seen this pair or had contact with them since December 17 please contact your local Police station immediately.

The white catamaran has blue anti-fouling paint under the waterline, measures 6 metres (21ft) in length and its sail ID number T878. Photo: Police