A strong earthquake has struck the greater Tokyo region. The quake hit after 4:00 a.m. on Thursday while most people were still asleep.

A strong earthquake struck the southern part of Chiba Prefecture, east of Tokyo, at around 4:16 a.m. Japan time on Thursday.

Officials with Japan's Meteorological Agency say there is no tsunami threat.

They estimate its magnitude at 5.2 and the focus at a depth of 40 kilometers.

Tremors of upper 5 on the Japanese seismic scale from zero to 7 were recorded in Kisarazu City in the prefecture. Lower 5 jolts were logged in Kimitsu City.

The officials are urging people in quake-hit areas to pay close attention to seismic activities.

Agency official Kamaya Noriko said the risk of falling rocks and landslides is rising in areas hit by strong tremors.

She warned a quake as powerful as upper 5 could strike over the next week in the areas where major jolts were recorded.

Another expert also warns that jolts of similar scale to the magnitude 5.2 earthquake in Chiba Prefecture that struck early Thursday may occur for about a week.

Professor Satake Kenji at the University of Tokyo's Earthquake Research Institute spoke to NHK.

He pointed out that the Pacific Plate from the east and the Philippine Sea Plate from the south move toward the Kanto region, which includes Tokyo. He said the region tends to see frequent seismic activity as a result.

Satake said he believes that the quake this time was likely triggered by movement of the Philippine Sea Plate, and such quakes often occur in the region.

The professor said tremors of similar intensity could hit the Kanto region for about a week.

He called on residents to remain on alert for possible strong earthquakes.