Tsunami warnings were issued for Fiji and New Zealand after a massive earthquake measuring about 7.8 in magnitude shook the southern Pacific Ocean.
The quake's epicenter was about 153 kilometers (95 miles) off the coast of Tonga, according to the U.S. Geological Survey.
It struck Thursday at 4:26 a.m in Tonga (Wednesday at 1526 GMT).
Two hours later, there was still no indication that a tsunami had been generated by the quake.
The geological center stressed that "it is not known that a tsunami was generated" by the quake.
"This warning is based only on the earthquake evaluation," it said.
Paula Chipman, an American tourist in Tonga's capital, Nukualofa, called it "a major, major shaker" and said it was impossible to assess the damage on the island because it was still dark.
"We felt it. We felt it huge," she said.
One guest at her hotel hurt his foot when he jumped from a balcony to get out, Chipman said.
"Everybody was bailing out of the building," she said.
Chipman said the area around her hotel was without power in the early morning darkness, except for several hotels -- including hers -- which were apparently running on back-up generators. Guests had heard "abosolutely nothing -- zero" from authorities on the island in the aftermath of the quake.
On the island of Fiji, to the west of Tonga, several people contacted by CNN reported no damage. One local journalist said he felt a tremor, but said the local seismologists had recorded a much weaker quake.
David Applegate, senior science adviser for the USGS, told CNN the earthquake was likely to affect only "a relatively small population."
"So far, we've got five responses in four city areas on the islands of Tonga, with intensities ranging from fairly light shaking up to very strong shaking," Applegate said.
The Pacific Tsunami Warning Center issued alerts for the islands of Tonga, Niue, American Samoa, Samoa, Fiji, and Wallis-Futuna.
The center's most recent report said a tsunami could have begun to affect the islands as early as 1600 GMT (noon ET).
An earlier warning for New Zealand was canceled, and an advisory for the Hawaiian Islands said only that coastal areas might experience "small sea level changes."
Applegate said the magnitude of the quake was larger than the 1989 temblor that struck the San Francisco Bay area, but "considerably smaller" than the December 24, 2004 quake off the Indonesian island of Sumatra.
That quake -- with a magnitude of 9.0 -- triggered a massive tsunami that spread across the Indian Ocean, killing more than 200,000 people in a dozen countries.