More tremors are likely following two earthquakes which hit central New Zealand, a GNS scientist says.

Seismologist Dr John Ristau said it was likely there would be more quakes following Thursday's shakes, but it was impossible to say whether they would be stronger or weaker than the 5.1.

"You have to remember this whole area is seismically active to begin with," he said.

"It's likely there's be an aftershock around 4. There's also a chance there'll be something bigger.

"If you think back to July 2013 when those quakes started you first had one around 5, a little bit above 5, and then a couple weeks later was the first of those two 6.6 quakes."

© Geonet