PORT MORESBY, Papua New Guinea (AP) — A powerful earthquake shook Papua New Guinea's northern coast Wednesday morning, sending residents fleeing for higher ground and items tumbling from shelves. There were no immediate reports of serious damage and no tsunami alert was issued.

Disaster authorities were struggling to contact residents of the small town of Aitape, near the epicenter. One Aitape local reached by the Australian Broadcasting Corp. said there had been no signs of unusual wave activity and no major damage.

The shallow, magnitude-6.8 earthquake struck about 19 kilometers (11 miles) east of Aitape. Max Kamave at the Aitape Resort Hotel told the ABC the tremor lasted for about three minutes and knocked stock off the shelves. Many residents, fearing a tsunami, ran for higher ground.

"They were all running around the street," he said. "They were frightened maybe the sea will come up."

Chris McKee, the assistant director of the Geophysical Observatory in the capital, Port Moresby, said people in the town of Vanimo, about 145 kilometers (89 miles) from the epicenter, reported they had also felt the quake strongly. There were no initial reports of damage or injuries.

The Pacific Tsunami Warning Center said there was no widespread tsunami threat but a quake of this strength could generate tsumani waves within 100 kilometers (62 miles) of the epicenter.

Kamave said there had been no unusual waves off Aitape since the quake, which struck at a depth of 13 kilometers (8 miles). Shallow quakes can potentially cause more damage at the surface.

Papua New Guinea is prone to seismic upheaval due to its location on the Pacific "Ring of Fire," an arc of volcanoes and fault lines encircling the Pacific Basin.

A magnitude-7.0 earthquake on the northern coast in 1998 generated a large tsunami that swamped Aitape and several other villages, killing about 2,200 people.