A bomb packed with nuts and bolts injured up to 50 young revellers on Friday at a huge outdoor concert in the Belarussian capital Minsk attended by President Alexander Lukashenko, officials said.
Interior Minister Vladimir Naumov said a second explosive device that failed to detonate had also been found at the same venue, the AFP reported.
Lukashenko, who has ruled Belarus since 1994, was at the concert at the time of the blast and visited the site within a few minutes, his press office said.
There was no immediate indication of who was responsible for the attack at the Independence Day concert, which occurred at 00:30 am (2130 GMT Thursday).
"An act of hooliganism took place at a gala concert in Minsk tonight. There was an explosion of an undetermined, apparently home-made device.... More than two dozen people have been injured," Minsk police said in a statement.
Naumov was quoted by Belarussian news agency Belta as saying around 40 people had been hurt and that three of them were in intensive care. Hospital officials said up to 50 people were injured.
Naumov also revealed that a second explosive device had been found and would help investigators in their inquiries on the bomb that detonated.
There were tens of thousands of people at the concert, mostly young people. The injured were taken to hospital in ambulances as police picked through the nuts and bolts that the bomb threw out.
"I felt a shockwave and suddenly blood started coming out of my leg. A bolt had gone into my leg. There weren't enough ambulances and my relatives had to take me to hospital in their car," Olga, 23 told AFP from her hospital bed.
Yelena Melnik, 28, added: "I remember that I wanted to make a call on my mobile phone and suddenly the phone flew out of my hand. I felt a shock but no pain.... The doctors had to take nuts out of my knee."
Interfax news agency quoted witnesses as saying they saw people with fingers and toes blown off in the moments after the blast.
"All the injuries are shrapnel wounds," Viktor Serenko, chief doctor at a hospital in Minsk that was treating seven of the injured, told AFP.
Igor Gurko, a doctor at another Minsk hospital, said they were treating 31 people injured in the explosion. Four of the injured being treated by Gurko and Serenko were in intensive care, the doctors said.
In comments broadcast on state television, Minsk police chief Anatoly Kuleshov said: "I think that the explosion was organised by a hooligan who didn't like our beautiful and well-organised party."
The country's nationalist opposition Belarussian People's Front, which fiercely opposes Lukashenko's rule, on Friday urged him not to use the explosion to further limit democratic freedoms in this former Soviet republic.
"It would be a major mistake if the authorities use this reprehensible event to further limit freedom and democracy and for a crackdown...," the deputy head of the party, Vintsuk Vecherko, told AFP.
The Belarussian president, who is backed by Moscow, rules the country with an iron fist and his regime -- lodged on the European Union's eastern border -- is considered "the last dictatorship in Europe" by the United States.