Friday night`s blaze in Bucharest started when a band performing at the club set off fireworks.
Demonstrators called for Mr Ponta to step down, complaining of government corruption and poor safety supervision.
Mr Ponta is already facing trial on corruption charges.
Romania PM Ponta resigns over fire
04 November 2015
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Romanian Prime Minister Victor Ponta has said he is resigning, a day after some 20,000 people took to the streets to protest against a nightclub fire that left 32 people dead.
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