More than 140 people were injured on Friday when gas-filled balloons exploded at a governing party campaign concert in the Armenian capital ahead of parliamentary polls on Sunday, officials said.
The emergencies ministry said 144 people suffered burns when scores of promotional balloons burst into flames at a concert staged by President Serzh Sarkisian's Republican party in Yerevan's central Republic Square.
Armenian internet sites showed a fireball rising into the air and chaotic images of people screaming in confusion and anger.
"The balloons exploded and caught fire after people holding the bunches released them from their hands into the air," a witness told AFP.
It was not immediately clear what caused the explosions although police said they were looking into various potential reasons including the "improper storage of flammable substances".
"All the victims had either medium or light injuries. Now doctors are trying to revive them from shock," Health Minister Harutiun Kushkian told reporters.
The promotional balloons were decorated with the governing party's election slogan "Let's believe in change".
The incident marred a largely calm election campaign and President Sarkisian promised a full investigation.
"I urge everyone to keep calm," he said.
"Let us pray for all the victims and wish them a quick recovery," he said in a statement."
Sarkisian's party has been tipped by opinion polls to triumph in Sunday's election ahead of its ruling coalition rival, the Prosperous Armenia party led by a wealthy former arm wrestling champion.
The vote is the biggest test of the ex-Soviet state's democratic credentials since disputed presidential elections in 2008, when mass rallies ended in bloody clashes between riot police and opposition supporters that left 10 people dead, casting a shadow over Sarkisian's administration.
The authorities in the mountainous country of 3.3 million people have promised an unprecedentedly clean contest for the 131-seat National Assembly in the hope of avoiding further political turmoil.
Opposition parties however have questioned the validity of the opinion polls and threatened demonstrations if there are mass discrepancies.