Warsaw residents are voting on whether to dismiss the mayor, a member of Poland's ruling party who had been accused by the opposition of a series of costly mistakes.

The referendum on Sunday was called by a member of the nationalist Law and Justice party at a time when opinion polls show it has more support than the ruling Civic Platform.

The ouster of Mayor Hanna Gronkiewicz-Waltz a year before her term expires would be a blow to Prime Minister Donald Tusk's pro-market government.

The opposition blames Gronkiewicz-Waltz for recent hikes in transport prices, botched reform of garbage collection and neglecting residents' needs.

A participation rate of at least 29 percent of Warsaw's 1.3 million eligible voters is required to make the vote valid. Turnout is expected to be low.