A magnitude 6.6 earthquake rocked western Japan late Wednesday night. No tsunami was triggered.

The tremor struck at around 11:14 p.m. It was strongest in the Shikoku region's Ehime and Kochi prefectures. Officials say it clocked a lower 6 on Japan's zero to seven seismic scale, making it the area's strongest quake since the current scale system was introduced in 1996.

Residents began clearing away the debris on Thursday. Roof tiles and walls were scattered across a shopping street in Uwajima City in Ehime.

Water pipes and utility poles were also damaged elsewhere. There have also been reports of debris blocking some roads.

Fallen rocks and trees forced JR Shikoku to suspend some train services through Thursday.

Authorities say only minor injuries, such as falls, have been reported. Some people were treated in hospital.

Nuclear power plants in the area are also stable. No major issues were reported at the Ikata nuclear plant in Ehime, nor at the Sendai plant in Kagoshima Prefecture. Radiation levels are said to remain steady at both.

The tremor resurfaced concerns about a potential mega-quake. This quake was centered in the Bungo Channel, which is part of the Nankai Trough. Experts expect a mega-quake in the trough in the next 30 years. But an expert says Wednesday's quake was probably unrelated.

The Earthquake Research Institute, the University of Tokyo's Professor Satake Kenji said he believes the cause of the earthquake differed from those in the Nankai Trough. He added that he thinks the quake came from the Philippine Sea Plate, which is sinking slightly.

Authorities are calling for caution, saying more quakes are likely to hit the region over the next week.