(CNN) — Four people, including two restaurant workers and two bystanders, were injured after a fire broke out after a suspected explosion in Tokyo on Monday, Japanese state broadcaster NHK reported, citing Tokyo police.

At around 3:15 p.m. local time, a witness reported seeing smoke coming out of a building window and hearing “an explosive noise”, NHK reported.

Video posted to social media showed a fire on the second floor of a building and debris strewn at an intersection.

All four are being treated for minor injuries, NHK added.

The restaurant – located in Tokyo’s central Shimbashi district – is believed to have been the source of the fire, NHK reported, citing Tokyo police.

The Tokyo Metropolitan Police is investigating the incident, according to NHK.