WELLINGTON (AFP) - A strong 5.6 magnitude earthquake hit New Zealand's South Island early on Tuesday morning, US seismologists said, but there were no immediate reports of damage or casualties.

The quake struck near the centre of the South Island at a depth of 10 kilometres at 6.48am local time (1:48 am Singapore time), the United States Geological Survey said.

The epicentre of the quake was located about 45 km from Methven, the nearest town, and 101 kilometres from the major city of Christchurch, according to USGS.

GeoNet, the New Zealand geological hazard monitoring service, classed the quake as severe, with more than 2,000 "felt reports" received by 2.30am Singapore time, some from as far away as the northern North Island.

Earthquake-prone New Zealand sits on the edge of the so-called Pacific "Ring of Fire", where continental plates collide, causing frequent seismic and volcanic activity.

The country experiences about 20,000 tremors a year, with an average of 2.5 of magnitude 6.0 or higher.

In 2011, 185 people were killed when a devastating 6.3-magnitude quake hit the South Island city of Christchurch in one of the nation's deadliest disasters of the modern era.

Wellington was the scene of the country's most powerful earthquake in 1855.

That 8.2-magnitude quake caused four deaths and changed the city's entire geography, pushing the shoreline out 200 metres as it thrust the harbour floor upwards.