Interfax said that police sources reported that up to 50 people had been wounded. Belarusian television said 36 had been hospitalised, and that six of them were in serious condition.
Alexei Murzhankov, a duty officer at the Vitebsk city department of the ministry, said that 25 of those injured in the blast on Thursday night had been hospitalised, four of whom were in intensive care.
Murzhankov said the explosion occurred just outside a city cafe.
A Vitebsk resident, Anton Stepanishchev, said the cafe was a temporary, partially open-air structure of the sort often set up to attract customers in the summer.
Public National Television said the bomb went off at a dance.
The cafe, in addition to offering food and drink, has a dance floor.
On Friday, the Interfax news agency reported that the explosive device in the Thursday night blast was buried in a flower-bed outside a cafe.
It was the second such explosion within two weeks in the town.
In the previous incident, a homemade bomb - a beer can stuffed with nails and metal scraps - was planted on 15 September in a flower-bed near a bus stop close to a theatre. That blast wounded two people.