A 4.6 magnitude earthquake struck 10 kilometres south of Havelock at 11.33pm last night, GNS Science says.
The 70km deep quake was felt in Marlborough, and was the second of two quakes that shook the South Island within a minute of each other.
It followed a 4.5 magnitude quake 10km southwest of Christchurch a minute earlier, 11km deep, and strongly felt in Christchurch, GNS Science said.
The strength of the 4.5 magnitude quake was revised down after earlier being reported as magnitude 5.0.
GNS seismologist Dr Bill Fry said it was possible that the shaking of the Christchurch quake had triggered the Blenheim quake, though they had occurred on different fault lines.
A police communications spokesman said there were no immediate reports of damage following the earthquakes.
- The Marlborough Express