There were no immediate reports of damage, and all tsunami warnings and watches were soon canceled.
Still, the alerts caused thousands of residents to flee to higher ground in at least three Pacific islands.
The Hawaii-based Pacific Tsunami Warning Center issued a regional tsunami warning for 11 nations and territories after a quake with a magnitude of 7.8 struck 183 miles northwest of the Vanuatu island of Santo at a depth of 21 miles. Two other quakes of magnitude 7.7 and 7.3 followed in the same area.
The center canceled the tsunami warnings after sea-level readings indicated that the wave generated by the quakes was too small to cause much damage.
There were no immediate reports of injury or damage from officials in Vanuatu, a chain of 83 islands. It lies just over 1,400 miles northeast of Sydney, Australia.
"We have no damage reports yet, but we have had no contact with Santo so far," Vanuatu police spokesman Take Rakau told The Associated Press from the capital of Port Vila on another island.
While the quakes were not felt in Port Vila, he said Santo island "most likely could have felt them."
In Tuvalu, a low-lying nation of eight coral atolls with about 10,000 people, thousands fled inland, some clustering around the government building in the capital, Funafuti - the only multistory building in the country.
"We've had a bulletin canceling the warning, and that has been broadcast," weather office head Hilia Vavae told The AP. "Even though nothing happened, it was a good exercise for us. We now can react and get to safety."
In Samoa, where at least 137 were killed in the Sept. 29 tsunami, the alerts Thursday caused thousands of people to "run for the hills," AP reporter Keni Lesa said from the capital, Apia.
"Thousands just dropped everything - people just ran for it," he said from the center of the city, shortly after the alert was canceled. "The word tsunami is a scary word here right now."
Before the warning was canceled, "it was so tense, you could cut it with a knife," he said. Cars clogged roads out of the city to the hills.
Thursday's warnings also created worry in American Samoa, where at least 32 people were killed and hundreds of homes destroyed in last week's tsunami. Residents of the coastal village of Utulei fled to the hills after hearing there was a tsunami watch for the U.S. territory.
Schools, government building and other residents were also evacuated to higher ground. Traffic was snarled in downtown villages of Pago Pago and Fagatogo.
Thursday's small tsunami came just over a week after a quake of magnitude 8.3 rocked the South Pacific near Samoa, sparking waves that killed at least 178 people and devastated coastal villages in Samoa, American Samoa and northern Tonga.
But seismologist Rafael Abreu with the U.S. Geological Survey in Golden, Colo., said the timing of Thursday's quakes was coincidental and the Vanuatu event appeared to be unrelated to the Sept. 29 quake. The quakes occurred on different fault lines and the way the earth's plates moved in both events also differed, he said.
The second quake Thursday, just 15 minutes after the first, hit at the same depth but 21 miles farther north of Santo and Port Vila. The third was recorded nearly an hour later, 175 miles northwest of Santo at a depth of nine miles.
Abreu said the second quake was originally measured at 7.3 but later upgraded to 7.7. The third was originally put at 7.1 but upgraded 7.3.
Also Thursday morning, the U.S. Geological Survey reported a strong earthquake struck south of the Philippines.
The quake had a preliminary magnitude of 6.7 and was located in the Celebes Sea, 175 miles southeast of Jolo, Sulu Archipelago, and 730 miles south of Manila. The quake hit at 5:41 a.m. Thursday local time.
USGS did not report any damages or injuries.