A powerful series of undersea earthquakes struck north-east of New Zealand on Friday, but tsunami waves that forced many people on the country’s North Island to flee to high ground passed without causing substantial damage, Reuters reported.

Officials had warned that waves could reach three meters (10 feet) above high tide levels after the quakes—the strongest a magnitude 8.1—but the threat had passed by the afternoon, the National Emergency Management Agency (NEMA) said.

Earlier on Friday, workers, students and residents in areas like Northland and Bay of Plenty, on the northern coast near Auckland, fled beachside towns for higher ground after the three quakes, striking in an eight-hour period, triggered blaring tsunami sirens and warnings to evacuate via text messages.

An emergency alert was issued for coastal areas around the country, with people to stay away from the water’s edge. There were no reports of damage or casualties from the quakes.

The third and strongest quake struck the Kermadec Islands, a mostly uninhabited group of islands some 800 km (500 miles) northeast of the North Island, on Friday morning, shortly after a 7.4 magnitude earthquake in the same region. Earlier, a large 7.2 magnitude earthquake struck just east of the North Island.