Small tsunami waves triggered by a series of powerful earthquakes hit the east coast of New Zealand's North Island on Friday and authorities said thousands of residents who had evacuated to higher ground could now return to their homes.

Officials had warned that waves could reach 3 meters (10 feet) above high tide levels after the quakes – the strongest a magnitude 8.1 – but the largest waves have now passed, the National Emergency Management Agency (NEMA) said as it downgraded the threat level.

"All people who evacuated can now return," the agency said.

Video footage posted on social media showed surges of water entering a marina in Northland and on the North Island's East Cape region.

Earlier on Friday, workers, students and residents in areas like Northland and Bay of Plenty, on the northern coast near Auckland, were put on alert after the three offshore earthquakes in less than eight hours triggered tsunami sirens and warnings.

Related story: New Zealanders urged to evacuate after earthquakes trigger tsunami warnings

The latest quake had a magnitude of 8.1 and struck the Kermadec Islands, northeast of New Zealand's North Island. This came shortly after a 7.4 magnitude earthquake in the same region. 

Earlier, a large 7.2 magnitude earthquake struck about 900 kilometers away on the east of the North Island.

There were no reports of damage or casualties from the quakes.

(With input from Reuters)