TOKYO -- The number of serious crimes recorded in Japan in the first six months of this year reached a record high of more than 10,000, while the arrest rate fell to an all-time low, the National Police Agency (NPA) said Friday.

Serious crimes such as murder, rape and arson, abduction and indecent assault increased by 16.6 percent from the same period last year to 11,304 cases, the NPA said in its latest six-monthly report.

But in the same period the arrest rate dropped four percentage points to 48.6 percent, the first time the rate has fallen below 50 percent since such records were first kept in 1989, AFP reported.

Recorded offenses committed by juveniles aged under 14 surged 87 percent to 137, according to NPA spokesman Shitsuno Yamauchi, while offences by minors aged between 14 and 20 increased 10 percent to 1,105.

Sexual crimes against children aged 12 or younger totaled 945, including 34 cases of rape -- also a record high, the NPA said.

"The increase in serious crimes committed by juveniles tells us that other measures in addition are needed," not just conventional policing, NPA Director General Hidehiko Sato told reporters in a briefing before the report was published.

While Japan remains one of the world's safest countries in terms of crime rate, the rising incidence of violent crimes and juvenile crime has spurred public debate on the causes and how to deal with the problem.

In July a 12-year-old boy admitted to abusing and killing a four-year-old boy, whom he pushed off an eight-story building in Nagasaki, southwestern Japan.