The municipal votes in Istanbul, Ankara and elsewhere are the first polls since a harsh police crackdown on demonstrators claimed eight lives last June and sparked months of political turmoil.
Erdogan, after more than a decade in power, has alienated many with his bellicose response, labelling his critics "terrorists", purging thousands of police and justice officials, and banning Twitter.
In weeks of frantic shirt-sleeves campaigning which has left his voice hoarse, he has declared the mayoral and local assembly elections a referendum on his Justice and Development Party (AKP).
"We will teach them a big lesson on March 30... and claim victory," Erdogan, 60, bellowed across a mass rally in Istanbul last week, one of scores of campaign events he has attended.
Erdogan, a former mayor of the megacity, intoned that "whoever wins Istanbul wins Turkey".
He has also vowed to quit politics unless his party emerges the winner.
Lowering the bar somewhat, the AKP has said any result over the 38.8 percent it won in 2009 local polls would be a success -- far below the 49 percent it scored in 2011 general elections.
Dozens of opinion polls have predicted AKP results ranging from less than 35 to more than 45 percent.
- Tight races -
Analysts stress that despite growing criticism of Erdogan as authoritarian, he still commands the loyalty of millions, as well as a rich campaign war-chest and an incumbent's grip on much of the national media.
"Erdogan is still a very skilled politician... and he exercises enormous control over Turkish institutions, giving him the ability to manage politics," said Brent Sasley, a Middle East expert at the University of Texas.
"I don't think we can quantify the loss he will receive at this point, but it's not likely to be enough to undermine his appeal within the party or among the electorate," he told AFP.
"If the AKP could lose a couple of big municipalities, I think there will be more boldness within the party to challenge him."
The race is predicted to be tight in Istanbul, the glittering prize, and especially in the capital Ankara, both long AKP strongholds where the main opposition Republican People's Party (CHP) now has stronger candidates than in recent polls.
The AKP will struggle to oust the opposition from key cities including Izmir in the west, a bastion of the secular CHP, and Diyarbakir, the largest city in the Kurdish-majority southeast.
- 'Coup plot' -
Though Erdogan is not on the ballot and many of the 53 million eligible voters will decide based on local issues, the poll is nonetheless the first test of the powerful premier's popularity since the turmoil kicked off by the June protests.
Erdogan faced another political nightmare when a major corruption scandal broke in December that saw dozens of leading businessmen and political figures, including the sons of three ministers, detained in police raids.
The crisis claimed the scalps of four ministers and prompted eight AKP lawmakers to resign.
Erdogan himself has been accused, based on leaked audio tapes purporting to be of tapped phone conversations, of conspiring with his son to hide millions of dollars in cash once the probe started.
The crisis has sent down the Turkish lira and stocks and rattled investors' faith in what has become a leading emerging market economy under Erdogan.
The premier has labelled the graft probe a "coup plot" by rivals, including former ally Fethullah Gulen, a US-based Muslim preacher who wields considerable influence in the police and judiciary.
Erdogan has embarked on a mass purge of police and prosecutors and pushed through draconian laws curbing the judiciary and access to online media.
Last week he banned Twitter, which was used to spread the audio recordings, raising international doubts about the health of Turkish democracy.
The ban was overturned Wednesday by an Ankara court.
Sunday's vote kicks off a busy electoral calendar, with a presidential poll due in August and a parliamentary vote scheduled next year.
Analysts say a poor result could scupper Erdogan's hopes of replacing Abdullah Gul as president and may prompt him to call early general elections or change party rules to allow him another term as premier.