Police say the risk of a flash flood on the Waimakariri River appears to have passed.
A large surge of water, visible from the air, was reportedly seen in the McLeans Island area moving down the river about 6pm.
Although river levels are high, the initial risk appears to have passed, police said.
However, police said river levels could still increase and requested that the low lying river banks on all Canterbury rivers by avoided.
The warning came after a day in which summer was turned on its head in southern and central regions.
Kaikoura residents reported seeing two twisters this morning.
Elsewhere, Southland residents were threatened by flooding, a bridge to Te Anau was washed out and firefighters were called to secure roofs in Wellington.