A magnitude 5 earthquake has hit near Seddon, but St John says it hasn't received any calls or reports of injuries from the area.
Geonet said the severe quake hit shortly after 4pm was 8km deep, about 30km south-east of the upper South Island town.
An office worker in Blenheim, Kelvin Deaker, said he did not feel it, but a few of his co-workers felt a light shaking.
The Marlborough District Council said people in Seddon had described it as a light to moderate shake.
St John is urging people in Marlborough to make sure they have emergency packs prepared, and to check on their friends, family and neighbours, especially those who are ill, frail or alone.