WELLINGTON (AFP) - A 6.6-magnitude earthquake struck off the coast of New Zealand Tuesday (July 11), officials said, with minor shaking in the South Island but no damage reported.

The quake beneath the ocean was estimated at a depth of 10km, more than 475km south of the mainland, the United States Geological Survey said.

No tsunami threat was issued.

"Based on the information we have there could be light to moderate shaking in the southern South Island," said Geoscience Australia duty seismologist Greg Breen. "But no damage is expected."

Several Twitter users in Invercargill and Dunedin said they felt some movement. But a Fire and Emergency New Zealand spokesman told the stuff.co.nz news website they had received "not one call for help".

New Zealand is on the boundary of the Australian and Pacific tectonic plates, which form part of the so-called "Ring of Fire", and experiences up to 15,000 tremors a year.