Osaka police said Wednesday they failed to report roughly 81,000 criminal cases to the National Police Agency between 2008 and 2012 — nearly 10 percent of the total number reported by the prefectural police force during the five-year period.

Osaka had seen the most bicycle thefts, muggings and other street crimes among the country’s 48 prefectures since 2000, but was thought to have been overtaken by Tokyo between 2010 and 2012.

The latest internal investigation has indicated, however, that Osaka remained the prefecture with the most cases of such crimes in the country throughout the years leading up to 2012.

The widespread nature of the underreporting undermines the credibility of the crime statistics compiled by the agency as a basis for devising measures to fight crime.

With underreporting found at all 65 of the force’s police stations, the Osaka police issued warnings and took other measures the same day against 89 officers, many of whom had been station chiefs or division heads during the five-year period. None, however, were subject to disciplinary action.

The latest probe showed that a total of 81,307 cases had not been reported to the agency during the period, against 838,156 cases that were reported.

Thefts accounted for 86 percent of the unreported cases, with nearly half involving bicycles. It was found that officers frequently failed to report cases in which stolen bicycles were found within a certain time period, determining that no harm was done.

In other cases, officers bundled multiple incidents of auto parts theft and similar crimes committed around the same time into single cases. Some officers said they had been instructed by their superiors not to report cases deemed minor, according to the police.

A senior Osaka police official has admitted that he felt “pressure” to erase Osaka’s reputation as the prefecture with the most cases of street crimes in the country.

The police launched the latest probe as doubts mounted over the outcome of their previous investigation — conducted after a discovery in June last year that a single officer had intentionally failed to report 6,585 cases between 2008 and 2012.

Masahide Yasui, a division head of the police force, said the underreporting has damaged the credibility of police statistics and was regrettable.

“We will strive to prevent a recurrence,” he said.