PORT VILA, Vanuatu?Three powerful earthquakes with magnitudes of 7.8, 7.7, and 7.1 struck near the South Pacific nation of Vanuatu in the space of just over one hour on Thursday, seismologists said.

The first magnitude 7.8 quake sparked a region-wide tsunami alert and was quickly followed by two other strong earthquakes, the United States Geological Survey said.

The initial earthquake struck 294 kilometers (183 miles) from Vanuatu's Espiritu Santo island at a shallow depth of 35 kilometers at 9:03 a.m. (2203 GMT Wednesday), and was followed just 15 minutes later by a 7.7 quake.

The second quake, the magnitude of which was revised upwards from 7.3, hit 330 kilometers from Luganville on Espiritu Santo island at 9:18 a.m.

Residents in the area were shaken again by a 7.1 magnitude quake at 10:13 a.m. about 280 kilometers (175 miles) northwest of Luganville.

Aftershocks also shook the region, with a 5.7 quake shaking Vanuatu nearly two hours after the first big quake, and a 5.3 tremor striking near Samoa, causing panic in the islands that were devastated by a tsunami last week.

A total of 184 people are confirmed dead in Samoa, American Samoa, and Tonga following a tsunami sparked by an 8.0 magnitude quake on September 29. Six remain missing.

The latest series of quakes and the region-wide tsunami warning caused panicked residents to flee to higher ground on Thursday, but experts said that waves measuring only between three and ten centimeters were recorded.