Homemade bomb wounds 50 in Belarus

About 50 people have been wounded by a homemade bomb that sprayed nuts and bolts into a crowd at an open-air concert in Belarus's capital, Minsk, attended by long-time ruler Alexander Lukashenko, officials say.

President Lukashenko, who has ruled the ex-Soviet state with an iron grip since the mid-1990s, was not far from the blast but was unhurt and did not appear to have been the target, his spokesman said.

A second, unexploded bomb had been found near the blast site, the interior ministry said. Police said its discovery should help their investigation.

The bomb went off in a big square in Minsk shortly after midnight (0700 AEST Friday), while thousands were attending the concert marking Independence Day.

A Reuters witness said the explosion left a pit 20cm deep, with blood splattered on the grass around it.

The interior ministry said three of the 50 injured were in a serious condition and doctors said they had treated dozens of people to remove shrapnel from their legs.

The injured were mainly young people, although they included at least two small children aged five and six.

Presidential spokesman Pavel Legkiy told Reuters Lukashenko "reached the site of the explosion within several minutes".

"This was not an attempted assassination on the president," he said. "That is my personal opinion, not as a specialist, but as a person who was at the scene ... Of course there can be a number of explanations and the truth will be established in the course of the investigation."

Officials said the blast was an act of "hooliganism" - a term commonly used by officials in ex-Soviet states to play down an incident's significance. There has been no known attempt on Lukashenko's life.

"I heard a loud explosion and there was black smoke," said 28-year-old Sergey, who did not give his second name. "People started shouting. No one stopped the concert. They just isolated the place around the explosion and emergency vehicles began coming."

The top doctor at a hospital which treated 31 of the injured said injuries were mostly caused by shrapnel in the legs.

"The condition of the majority is satisfactory," he said. "We undertook 26 operations to remove nuts and bolts. Unfortunately, the majority of the injured were youths."

In 2005, a homemade explosive device wounded more than 40 people in the northern city of Vitebsk. A little known, anti-Lukashenko group, The Belarussian National Liberation Army, later claimed responsibility but no one was convicted.

The opposition said it was worried the blast could be used against them.

The liberal United Civic Party called on authorities "to refrain from the temptation to use the incident to conduct parliamentary election campaign under emergency conditions and to organise a crusade against political opponents".

The West has accused Lukashenko, a close Russian ally, of gagging independent media, quelling protests and incarcerating opponents. The European Union and the United States have banned him from entry, saying he rigged his re-election in 2006.

Lukashenko argues he has helped save Belarus from the political and economic chaos of other ex-Soviet states and remains broadly popular in the country of 10 million, wedged between Russia and Poland.

Some EU states have said a fair election, due in September, could transform relations with Minsk, but the continued imprisonment of an academic who ran against Lukashenko in the 2006 poll remains the key stumbling bloc for better ties.