Residents in the capital, Nuku'alofa, 120 miles (195 kilometers) southwest of the epicenter, said their homes rattled, and the tremors set off frantic barking of dogs.
"There's no indication of damage right now in this area," said Faleo Vico, the duty Weather Office staffer in Nuku'alofa.
In the town of Ha'apai, on an island 185 miles (300 kilometers) northeast of the capital, resident Lano Fonua said the quake was strong and lasted about 45 seconds.
"Many people went out into the streets as the quake was shaking the area quite a bit. It was really going," he said.
The U.S. Geological Survey said the quake, which struck at 3:32 a.m. (1332 GMT, 8:32 a.m. EST), was 6.8-magnitude and was generated from a depth of 38 miles (62 kilometers) in the ocean. No tsunami was reported.
"I felt the quake myself. It's not the worst that I've felt here, not by a long chalk," Tonga police commander Chris Kelley said.
On Sept. 29, a tsunami spawned by a magnitude-8.3 earthquake killed 34 people in American Samoa, 183 in Samoa and nine in Tonga.