The amount of stimulant drugs seized by police soared to 550.1 kg from January to June, about 3.4 times the amount seized in first half of 2012, the National Police Agency said Thursday.

Even though that total was for only six months, it is the first time in 13 years the annual amount has exceeded 500 kg.

Of the total, 430 kg were confiscated by police in Tokyo and Hyogo Prefecture, near Osaka.

The street value of 1 gram of stimulants stood at ¥90,000 in 2009 but has fallen to ¥70,000 today, the NPA said. "Drugs may have been spreading in Japan with an increase in inflow. We will tighten controls at the borders," an NPA official said.

Of the amount seized in the first half, 99 percent was found as it was entering the country.

Police investigated 48 smuggling cases involving stimulants in the period, a drop of four from a year before. The number of people involved in the cases fell by eight to 62, the NPA said.

In 10 cases, the drugs were smuggled from Mexico, while there were four cases each of drugs coming from mainland China, Kenya and Canada. There were two cases each originating in Hong Kong, India, United Arab Emirates, Turkey, South Africa and Uganda. The NPA statistics did not break down the countries or regions of the remaining 14 cases.

The total number of police cases involving smuggling, use or possession of stimulant drugs reached 7,104 in the half, down 810 from the first half of 2012, while the number of people involved totaled 5,136, down 524.

In the 7,104 cases, a total of 5,136 people were involved, among which 2,686 people, or 52.3 percent, were members of crime syndicates, the report said.