The Hawke's Bay town of Wairoa has been rocked by more than 20 earthquakes in the past 24 hours - a pattern that could be in play for days, scientists say.



According to Geonet, the strongest shakes only measured "light" on the intensity scale but the tremors were unlikely to let up for a couple of days.



Geonet data centre manager Kevin Fenaughty said the event was known as an "earthquake swarm."



Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time.



"This activity really burst into life yesterday evening soon after 5.30pm, with six noticeable quakes occurring within 45 minutes," he said.



Since then, further pulses of activity were recorded between 9.45pm and 10pm, 12.45am and 1.45am, and most recently between 7.20am and 9.30am.



A 4.8 was recorded at 7.21 this morning, at a depth of 67km, just 40km south of Wairoa.



According to reports, it was felt as far north as Waitoa, near Morrinsville, and as far south as Poukawa, below Havelock North.



Fenaughty said the duration of a swarm could not be predicted, but past experience with this part of New Zealand suggests that this one is of the order of days.



It could then recur at a later date after a break in the activity.



Another characteristic of swarms was that no single earthquake in the sequence was obviously the main shock.



It is unlikely the quakes would get bigger than the 4.8 recorded to date, but it could not be ruled out, Fenaughty said.