Police say a man who sparked a tsunami alert at a North Canterbury beach was confused by an optical illusion.
Whitebaiters and others at the beach at Kairaki, near Kaiapoi, scrambled for safety on Friday after the man drove along the beach area tooting the horn of his car and yelling "Tsunami coming".
Most people left the beach area immediately, causing a traffic jam on the road to Kaiapoi.
However, police say there was never any danger of a tsunami.
They say a combination of distant sea fog and light refraction made several people think a large wave was coming into shore.