Canterbury Police say they have “strong lines of inquiry” into the cause of the overnight fire which started at Pegasus beach, north of Christchurch.
Police inspector Peter Cooper said locals helped police identify people of interest, who might be able to explain how the huge 200-hectare fire started.
The fire is believed to have started on Pegasus Beach, just beyond the beach carpark.
“Fireworks may have been involved and that is something we’ll look into today.”
A Coastguard North Canterbury spokesman told Chris Lynch they’re also assisting with the fire fighting at Pegasus.
“Our role is to be standing by at sea as rescue services for Helicopters operating.
They are at risk when taking dips into the sea to fill their buckets.”
There was also high winds in the area.
Five helicopters with monsoon buckets are dropping thousands of litres of water on the Pegasus fire and are being joined by two fixed wing aircraft.
Incident Controller Dave Berry said “we aim to make as much progress as possible before wind speeds increase again today.
Seven ground crews are working on the flanks of the fire, supported by tankers.
The command unit and a full incident management team are operating from Woodend.
No homes or other buildings are known to have been damaged by the fire and we are aiming to get evacuated residents back home in a managed way when it’s safe.
Canterbury Public Health is expected to release health information this afternoon.