Swarm of quakes rattles South Island

A swarm of earthquakes has rattled the South Island but seismologists don't believe there is any cause for alarm.

The latest quake struck just before 3pm and was centred in the Christchurch suburb of Cashmere. It measured 3.9 on the Richter scale but was strongly felt across the city as it occurred at a depth of just 5km.

There were no immediate reports of damage from the quake but it left residents rattled as it was the first big aftershock to hit the city in some months.

Online notice boards immediately lit up with comments from residents spooked by the quake: ''Biggest felt in ages,'' one poster wrote. ''The noise was huge,'' said another.

''I have been waiting for another biggie, let's hope it isn't a foreshock but just in case I am filling my water bottles and getting things ready,'' another person said.

British actress Miriam Margoyles was doing a matinee performance of her show Dickens' Women when the quake hit but continued with the show, apparently unfazed by the rumbling beneath her feet.

''She paused briefly as the audience gasped and then continued without skipping a beat,'' said Ali Jones, who was in the auditorium watching the show.

''The whole building really shook and there was quite a bit of noise with it.''

Earlier in the day Southland was struck by two quakes, the largest of which measured 5.5 and was centred 40km west of Tuatapere at a depth of 12km.

Craig Rutland, who runs the backpackers at Tuatapere, said the ground shook vigorously but it was not a violent quake.

''It was very strong but nothing was thrown off the walls or fell off the shelves,'' Rutland said.

One of his guests was just sitting down to breakfast when the quake struck at 10.07am and was a bit unnerved by the experience. When it started we were a bit worried about what was going to happen, Rutland admitted, but it dissipated pretty quickly.

Others spoken to in the small Southland settlement reported the quake as a fairly big rumble but said they were unaware of any damage occurring as a result.

The quake was preceded by a magnitude 2.8 quake centred in roughly the same area.

A magnitude 4.3 quake also struck the Kaikoura region this morning. It was centred 30km east of Kaikoura at a depth of 15km.

GNS seismologist Mark Chadwick said it was not unusual to see so many earthquakes in one day and it was unlikely the quakes were a forerunner to a more significant seismic event.