Glitches in a new earthquake alert system have seen erroneous reports, based on early data, of massive earthquakes sent out.

GNS Science's GeoNet Data Centre, which is using a newer and faster automated alert system, sent out email alerts on Thursday morning, initially reporting a 5.6-magnitude quake off Auckland's west coast and a 6.4 quake off Taranaki.

However, both turned out to be a rather more moderate 2.7 and 3.7 quakes near Oxford in Canterbury.

A GNS seismologist said the Auckland report was actually the combined data from a distant earthquake in the Pacific and the first Oxford quake, which happened at the same time.

The initial reports of the larger earthquakes came with a caution and the size and location of the quake was firmed up as more information came in, she said.

Following the history of a quake on the GeoNet website was a more accurate guide to the earthquake, she said.