TOKYO — A powerful earthquake rattled southern Japan on Sunday, swaying buildings and briefly prompting warnings of tsunami. At least 66 people were injured and smaller aftershocks continued to rattle the region.

The magnitude-7 temblor, which hit west of Kyushu Island at 10:53 a.m. local time, was centered at an "extremely shallow" depth below the ocean floor, the Japanese Meteorological Agency said. An hour after the initial earthquake, aftershocks followed — at least one a magnitude-4.2 quake.

Within minutes, the agency warned of the possibility of 20-inch tsunami waves triggered by the seismic activity, and cautioned residents near the water to move to higher ground. But an hour after the quake, the agency said there was no danger of tsunami.

"There may be some disturbance of the ocean's surface, but we aren't worried about tsunami damage," said Masahiro Yamamoto of the Meteorological Agency.

At least 66 people, most in hard-hit Fukuoka prefecture, were injured by the quake, some struck by toppling cabinets, items falling off shelves or shattered glass, and one burned by a cooking stove, public broadcaster NHK TV said.

In Okawa city, a 56-year-old man suffered broken bones after trying to jump to safety from the second floor of his home, the network said.

One person was reportedly pinned inside a collapsed home.

Officials reported water main breaks, and the possibility of power blackouts. Local and bullet train railway service was halted, after an automatic safety mechanism was triggered by the tremors, NHK reported. Telephone service in the southern prefecture was overwhelmed and jammed.

About 100 residents of Genkai, a tiny island off the coast of Kyushu, were evacuated after homes collapsed and roofs caved in, and village officials requested emergency help from Japanese troops, NHK said.

Local officials in Fukuoka, about 562 miles southwest of Tokyo, told NHK that the shaking, which lasted as long as 30 seconds, toppled desks and knocked books off shelves and made it difficult to stand.

NHK showed tall office buildings and street lamps in the center of Fukuoka, nearest the epicenter, shaking violently. In residential areas, cracks appeared in sidewalks and parts of retaining walls flaked off.

Authorities warned of landslides around the states of Fukuoka, Saga and Nagasaki.

Kyushu Island is separated from South Korea by a narrow strait of water, and the quake was felt about 130 miles away in South Korea's port city of Busan, where it briefly shook buildings. No damage was immediately reported, a police spokesman in Busan said.

Located along the Pacific Ocean's seismically active "Ring of Fire," Japan is one of the world's most earthquake-prone countries. A magnitude 7 quake can cause tremendous damage in populated areas, either directly or by triggering tsunami, which are distinguished from normal coastal surf by their great length and speed.

On Oct. 23, a magnitude-6.8 earthquake struck Niigata, about 160 miles northwest of Tokyo, killing 40 people and damaging more than 6,000 homes. The jolt was the deadliest to hit Japan since 1995, when a magnitude-7.3 quake killed 6,433 people in the western city of Kobe.

On Dec. 26, a 9.0-magnitude quake triggered a massive tsunami that devastated Asian and African coastlines in nearly a dozen nations, killing at least 175,000 people.