At least 20 people sustained injuries after a man sprayed an unidentified liquid inside a luxury shopping mall in Tokyo on Monday.

Police said the man, who was not named, sprayed the pungent-smelling substance at an ATM on the ground floor of Ginza Six in central Tokyo.

The incident triggered a massive emergency response, with police and firefighters sealing off roads around the building in the upscale shopping district. Police said they mobilised 53 fire trucks and blocked passage around the mall, and kept more than 10 emergency vehicles and ambulances on standby.

Police found 25 people who complained of sore throats and other symptoms following the incident, NHK World reported. At least 19 people were taken to hospital for treatment.

Firefighters dressed in hazmat suits were seen taking people from the mall into specialised trucks to examine them.

A woman in her 70s who was at the scene told the broadcaster that her throat started "stinging and hurting" as she approached the ATM.

"By the time I arrived, the commotion had already started, and I thought there might have been a small fire or something," she said.

"Once I went into the ATM corner, my throat felt scratchy, almost numb. Even now, I still feel a choking pain."

Eyewitnesses described the suspect as a man wearing a long-sleeved black shirt with white pants and a white mask.

Police were investigating the cause of the incident, a fire department official told the AFP news agency.

It was the second incident in less than a month involving people in Tokyo taking ill from a gas sprayed in a public area.

On 10 May, at least 10 people were taken to hospital after an unknown substance was reportedly sprayed inside a moving train near Tokyo.

The train was going from Odawara in Kanagawa prefecture to Takasaki in Gunma when passengers reported a strange smell inside one of the cars. Some passengers began coughing and complained of throat irritation and breathing difficulties, local media reported.

The incidents have revived memories of the 1995 sarin gas attack. At least 14 people died and over 5,800 fell ill after members of the Aum Shinrikyo cult released sarin gas on trains over 30 years ago.