Forty bottles of hot sesame oil shipped by air from Hong Kong last September were found to contain around 8 kg of a liquefied stimulant dyed red, police said Wednesday.

The substance was described as a kakuseizai stimulant, the main ingredient of which is amphetamine or methamphetamine. The shipment was made by express mail to Narita airport east of Tokyo. When synthesized into powder the stimulants would have had a street value of ¥700 million, the police said.

The shipment was addressed to a Taiwanese restaurant in Tokyo's Shinjuku Ward. Police searched it, among other places.

They arrested a 59-year-old Chinese man, Zhang Kai, for allegedly producing around 190 grams of stimulant drugs at his home in Shinjuku between February 2012 and last November. He is suspected of involvement in the smuggling of the liquefied kakuseizai.

Police said they confiscated a manual for manufacturing drugs from his home. Zhang has denied producing drugs, they said.