Last updated 17:20 06/03/2011
The earthquake struck at 4.43pm, 20 kilometres east of Kaikoura at a depth of 12km. The earthquake was widely felt on the east coast of the South Island, the GeoNet website reported.
Police spokeswoman Alli Dunn said the rockfall was about 10km north of Kaikoura.
Motorists were urged to take care driving in the area while authorities worked to clear the road, she said.
Further south, five aftershocks of magnitude 3 and stronger shook Christchurch and surrounding regions today.
There have been frequent aftershocks since February 22's deadly 6.3 quake that devastated parts of Christchurch.