WELLINGTON -- At least two people are believed to have died in a severe earthquake that rocked much of New Zealand just after midnight Monday.

Police and other emergency services were trying to reach a property at Mount Lyford, north of Christchurch, on the east of the South Island, where at least one person was believed to have died.

A Police statement said another casualty had been reported at a collapsed property in Kaikoura, on the northeast coast of the South Island.

The magnitude 7.5 earthquake was centered 15 kilometers northeast of Culverden, on the east of the South Island, and struck at 12:02 a.m. on Monday, according to the government's GeoNet monitoring service.

The quake was 15 km deep and was felt widely throughout New Zealand.

It is being followed by many aftershocks, the largest of them a magnitude of 6.2.

The Ministry of Civil Defence and Emergency Management (MCDEM) issued a tsunami threat along most of the country's eastern coasts after the initial earthquake and urged residents to move to higher ground.

The first tsunami waves had arrived, but it was too early to know what damage or casualties there might have been, said a statement from the MCDEM.

"Further waves should be expected and may be larger or more dangerous," it said.

It urged people to stay off beaches, stay out of the water, and not go sightseeing.