Ten people were reportedly taken to a hospital in Japan on Sunday after reports of an unknown substance being sprayed inside a moving train near Tokyo.

The incident occurred at around 4.30pm on 10 May on an East Japan Railway Company (JR East) train operating on the Tokaido Line section. The train was travelling from Odawara station in Kanagawa prefecture to Takasaki in Gunma when passengers reported a strange smell inside one of the train cars.

Some passengers began coughing and complained of throat irritation and breathing difficulties, local media reports said.

The train made an emergency stop at Kawasaki station in Kanagawa prefecture, where firefighters and emergency personnel inspected the affected carriage.

More than 20 ambulances and emergency vehicles were reportedly dispatched to the station following the alert.

According to Tokyo Weekender, a woman in her 30s called emergency services shortly before 4.40pm to report that an unidentified substance had been released inside the train. She, her husband and their one-year-old daughter were later taken to hospital, though none suffered serious injuries. It reported that some passengers in the same train car as the family complained of a strange pepper-like smell.

Initial reports said around 10 passengers were hospitalised after falling ill. However, later updates from police cited by Kyodo News focused on the family of three among those receiving medical attention.

No witnesses reported seeing any substance being sprayed inside the train, according to The Japan Times, and firefighters found no hazardous readings during gas inspections. However, several passengers said they noticed a smell similar to pepper.

The nature of the substance remains unknown.

Investigators later said no harmful gas was detected during inspections, and authorities had yet to determine whether any substance had actually been sprayed inside the carriage.

JR East temporarily suspended inbound Tokaido Line services between Yokohama and Shinagawa following the incident, with some trains later rerouted via Yokosuka Line tracks as operations gradually resumed.

Officials have not released details about the suspected substance, and the extent of the passengers’ injuries remains unclear.