The grandparents of NZ triplets killed in a fire at a daycare centre in a Doha mall are travelling to Qatar to support their grief-stricken mother and father.

Police are investigating separate house and garage fires at a Nelson property overnight.

Twelve fire trucks were sent to Diocesan School for Girls in Auckland this afternoon after a fire broke out in an air conditioning unit.

Firefighters are battling a suspicious house fire in the Auckland suburb of Mangere East.