TOKYO, June 21 (Xinhua) -- Japan's Osaka prefectural government said Thursday it had decided to inspect all concrete walls made of blocks in the area after a nine-year-old girl was crushed to death Monday after a strong earthquake caused the outer wall of her school's swimming pool to collapse.

Local investigators suspected her death may have been a result of professional negligence as certain parts of the wall's construction seemed not to have met legal standards including its insufficient reinforcement.

"We cannot rule out the possibility of human error that led to the girl's death," Takatsuki Mayor Takeshi Hamada said.

He made the remarks on Thursday morning after he placed flowers in front of Juei Elementary School where the nine-year-old victim used to study. "I feel sorry for the victim," he added.

Japanese Prime Minister Shinzo Abe also went to the quake-hit prefecture Thursday and visited the site where the girl lost her life and other hard-hit locations in the region.

"I want to ensure school safety by carrying out emergency inspections across the country," Abe was quoted as telling a press briefing.

"We must prevent a recurrence of this kind of tragedy," the Japanese premier said.

As a result of Monday's quake, around 417 buildings at public kindergartens, elementary, and junior high and high schools have been damaged, according to reports received by local authorities.

The strong quake claimed the lives of at least five people and injured more than 480 others.

More than 1,000 people sought refuge in emergency evacuation centers as of Thursday morning as heavy rain has raised the risk of potentially fatal mudslides.

More than 800 homes have been damaged, local authorities also said, and many remain without gas, forcing their inhabitants to rely on bread-based products and microwavable food.

Monday's quake was the biggest to hit the Kansai region since a magnitude-7.3 quake leveled Kobe in Hyogo Prefecture in 1995, claiming the lives of more than 6,000 people.