© The NZ Herald
There have been no reports of damage so far, but workers in the central city have described multi-storey office buildings swaying for at least 30 seconds as the quake hit at 9.06am.
GeoNet said the "severe" quake struck 30km east of Seddon, in Marlborough, at a depth of 8km.
There has been a flurry of smaller shocks since the initial magnitude 5.7 quake, the strongest recorded as magnitude 3.8 at 9.38am.
At least 10 other shocks were recorded in the Marlborough area by 9.45am.
A Fire Service central communications spokeswoman said there were no reports of damage in the Wellington region so far, although an alarm activation may have been caused by the quake.
The quake shook the emergency services communications centre on the seventh floor of the police station on Victoria St in central Wellington for a good 30 seconds, she said.
There have also been no reports of damage in the upper South Island, a Fire Service southern communications spokesman said.
