An unspecified number of people also were killed in neighboring Samoa.
The eartquake had a magnitude of up to 8.3 as it struck between Samoa and American Samoa around dawn Tuesday, sending terrified residents fleeing for higher ground.
The quake hit at 6:48 a.m. Tuesday (1748 GMT) midway between the two island groups. In Apia, families reported shaking that lasted for up to three minutes. The U.S. Geological Service, which estimated the magnitude at 8.0, said the quake struck 20 miles (35 kilometers) below the ocean floor, 120 miles (190 kilometers) from American Samoa and 125 miles (200 kilometers) from Samoa, with a 5.6-magnitude aftershock 20 minutes later.
The Pacific Tsunami Warning Center put the quake's magnitude at 8.3 and issued a general alert for the South Pacific region, from American Samoa to New Zealand. It said there were indications a tsunami wave could be "destructive" along some coastlines. Several hours away from the epicenter, Hawaii was put under a tsunami watch, with five emergency centers opened as a precaution.