TOKYO (AP) — More than 20 people developed sore throats near a luxury department store in Tokyo’s posh Ginza shopping area on Monday after a person allegedly sprayed an unknown substance, Japanese fire department officials said.

The Tokyo Fire Department said 26 people complained of suddenly developing throat pain and felt unwell near the Ginza Six shopping complex, and all but one of them were taken to a hospital. Their symptoms were believed to be mild, officials said.

Fire department and police officials said an investigation was underway. The largest-circulation Yomiuri newspaper said police have detected traces of pepper spray on the wall.

Dozens of fire engines and ambulances were parked outside the complex, and the surrounding roads were temporarily closed. Television footage showed firefighters and officials in hazmat suits assisting people, with some being brought out of the building.

Yuzo Tsuda, a 78-year-old Tokyo resident, told The Associated Press that he walked toward the shopping complex after having lunch with friends, drawn by the commotion, when he suddenly felt pain in his throat and started coughing. He said the ache in his throat subsided about an hour later and he did not plan to go to the hospital.