A shallow, powerful earthquake struck off the northeastern coast of New Zealand on Thursday, with officials warning of a possible tsunami threat. There were no immediate reports of serious damage or casualties.

The quake measured a preliminary 6.9 magnitude and was centered at a depth of 10 kilometers (six miles) about 178 kilometers (111 miles) northeast of the city of Gisborne, the U.S. Geological Survey said. Residents of Gisborne reported light to moderate shaking, it said.

New Zealand's National Emergency Management Agency said it was still assessing whether the quake had triggered a tsunami that could affect the country. It measured the quake at magnitude 7.3.

A magnitude 6.3 quake in 2011 hit the city of Christchurch, killing 185 people and destroying much of its downtown.