The polls pose a major challenge for Turkish President Recep Tayyip Erdogan and his Justice and Development (AK) Party given a backdrop of high inflation and rising unemployment sparked by a major currency crisis last year.
According to Taha Akyol, a Turkish political analyst and columnist, the vote is the "hardest" faced by Erdogan's party since coming to power in 2002.
"The party is trying hard to stay away from discussing actual economic issues," he said.
Turkey's economy has been hit hard since the lira lost as much as 40 percent of its value against the US dollar last year. The currency crisis, triggered in August after a bitter diplomatic spat with Washington, raised investor concerns over the independence of the Central Bank and highlighted wider worries over the performance of the economy.
Voting has started in Turkey's eastern cities at 7am (05:00 GMT) and will end at 4pm (14:00 GMT). Citizens in Western cities will vote from 06:00 GMT until 15:00 GMT.
The polls take place just weeks after official statistics showed that in the last two quarters of 2018 the Turkish economy slipped into its first recession in a decade, as inflation and interest rates soared due to the currency meltdown.
In February, inflation stood at just under 20 percent, while the Central Bank's main interest rate is currently 24 percent.