An earthquake near New Zealand's North Island has shaken the city of Gisborne and caused at least three buildings to collapse.

The 6.8 magnitude quake struck late Thursday 50 kilometers off the island's east coast. The quake was followed by at least one aftershock Friday morning.

Seismologist Warwick Smith says he expects more minor aftershocks.

Authorities declared a state of emergency and cordoned off Gisborne's city center while they assessed damage.

Eleven people were treated for minor injuries.

Some information for this report was provided by AFP, AP and Reuters.