The device went off last night on Pokrovka Street, a trendy area in central Moscow dotted with bars and restaurants.
"A hooliganism inquiry has been opened," Moscow police spokesman Maxim Kolosvetov said.
Preliminary information suggests the makeshift explosive was thrown either from a car or a nearby residential building and hurt "several" people, another Moscow police spokesman, Andrey Galiakberov, told AFP.
Smashed glass could be seen at the bus stop and several police cars, fire engines and an ambulance were at the scene, a correspondent reported from the scene last night.
"I first thought there were people shooting and I ran away from the bus stop," she said.
