WELLINGTON: A strong magnitude-6.1 earthquake rocked southern New Zealand Wednesday, one of three quakes to hit the region in four hours and the latest of hundreds of aftershocks since a massive 7.8-magnitude quake last month, seismologists reported.

Emergency services and police in the southern city of Invercargill said there were no immediate reports of injuries or damage from the quakes Wednesday in the Fiordland region of South Island.

Government seismology agency GNS Science said it measured the quake at magnitude 5.9 but it was registered at 6.1 by the U.S. Geological Survey in Hawaii. Geologists say quake measurements are often more accurate at greater distances because of how shock waves travel through the Earth.

The quake off South Island's west coast was centered at a depth of six miles (10 kilometers) and was one of the biggest aftershocks since the 7.8-magnitude quake hit July 15, the strongest earthquake recorded in the world this year, seismologist Lara Bland said.

Two quakes hit earlier in the day, one registering magnitude 5.2 and the other 4.8, GNS Science reported on its Web site.

Geologists said late last month that the power unleashed by the quake twisted South Island out of shape, moving its southwest tip 12inches (30 centimeters) closer to Australia.

It also generated a small local tsunami about eight inches (20 centimeters) high.

New Zealand's Earthquake Commission said last week that the damage from the big quake and its aftershocks could rise to NZ$6 million ($4 million).

The country sits above an area of the Earth's crust where the Pacific and Australian tectonic plates collide. It records more than 14,000 earthquakes a year, though only about 150 can be felt by people and fewer than 10 a year do any damage. LINK