People are being urged to stay away from the Hapuku River as a 150m-high dam threatens to fail.
The Canterbury Civil Defence Group this morning advised the dam could "rapidly fail" because of recent heavy rain and rising pressure, spilling water and debris from a newly formed lake over or through the dam.
"We strongly advise people to stay away from the riverbed, especially as the situation could change quickly with further earthquakes and/or rainfall," the group warned.
Police and others have been out identifying any campers and residents in the area and warning them to stay clear of the river and moving anyone on that is in harm's way.
The Hapuku River begins in the Seaward Kaikoura Range and flows south-east to enter the South Pacific at Hapuka, between Clarence and Kaikoura.