Osaka and nearby prefectures in western Japan on Wednesday marked one month since a strong earthquake in the region that killed four people, including a schoolgirl, and injured over 400.

The magnitude 6.1 quake on June 18 destroyed tens of thousands of homes and forced more than 2,000 people to take shelter in Osaka, while disrupting utility supply lines and traffic in the area, which was subsequently pounded by torrential rain that caused widespread landslides and flooding.

At an elementary school in the city of Takatsuki, Osaka, teachers and municipal officials offered silent prayers at 7:58 a.m., the moment when the quake occurred. One of its pupils, 9-year-old Rina Miyake, was crushed to death after a concrete wall around the school collapsed when she was on her way to school.

"A sense of guilt for failing to protect the precious life and deep sorrow remain unchanged a month after the quake," said Yoshimi Tanaka, principal of Juei Elementary School.

The collapse of the substandard wall has prompted the government to instruct owners of such walls nationwide to check their safety.

4 dead, over 300 injured as M6.1 quake hits Osaka area

At the Takatsuki city office where about 100 officials observed a moment of silence, Takatsuki Mayor Takeshi Hamada said, "We will strive to create a safe city through such efforts as removing concrete block walls."

The earthquake also caused serious traffic disruptions that blocked emergency vehicles and stranded people on their way to and from work or school.

The Osaka prefectural government on Wednesday launched a committee to beef up anti-quake measures and discussed ways to prevent similar traffic chaos, as the area is predicted to be hit by a massive earthquake within the next 30 years along the Nankai Trough extending from off the coast of central Japan to the southwest.

The committee made up of experts on economy and disaster prevention evaluated the case of the June quake in Osaka and surrounding regions, which caused the suspension of transport on railways and expressways, and severe traffic jams.

Yoshiaki Kawata, who heads the committee, said, "The quake was the world's first that struck a major city during the morning rush hour."

"We have to quickly learn and compile lessons by discussing challenges," and prepare for the potential earthquake in the Nankai Trough which it is estimated will be as strong as magnitude 9.1, Kawata said.