The emergencies ministry said that 144 people suffered burns when several promotional balloons exploded at a showpiece 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 after thousands of Republican party supporters celebrated with big bunches of balloons at the concert.
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"The balloons exploded and caught fire after people holding the bunches released them from their hands into the air," an eyewitness who asked to remain anonymous told AFP.
It was not immediately clear what caused the incident.
"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".
President 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 super-rich 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 falsifications.
