UPDATE 1-Traffic gridlock as Turks rush back to Istanbul to vote in high-stakes poll

(Removes reference to TV video from media identifier line)

By Ezgi Erkoyun and Daren Butler

ISTANBUL, June 23 (Reuters) - A re-run of Istanbul's high-stakes mayoral election has kept Turkish airports, bus stations and main highways jam-packed over the weekend, as voters rush back to the city from vacation or their original home towns to cast their ballot.

Some 10.5 million people were eligible to vote in Sunday's election, which has become a referendum on President Tayyip Erdogan's policies and a test of Turkey's ailing democracy.

"We all made great efforts to bring in those from outside Istanbul (to vote)," Erdogan told reporters after casting his ballot. "(There is) work on sending them back from here to their home provinces... Presumably the turnout will be very high."

The stakes are high for Erdogan and his ruling AK Party (AKP), which demanded the re-run citing voting irregularities after the main opposition party's candidate, Ekrem Imamoglu, won the original municipal election on March 31 by only about 13,000 votes. Turnout then was 84.7 percent.

Both the AKP, whose mayoral candidate is former Turkish prime minister Binali Yildirim, and Imamoglu's Republican People's Party (CHP) have spared no effort to get their supporters to polling stations, knowing that every vote counts.

Planes, buses and ferries heading to Istanbul, Turkey's biggest city and commercial hub, were operating at full capacity, Anadolu state news agency said.

More than 3,000 buses have arrived at Turkey's main bus terminal from across the country, Birol Ozcan, the head of Turkey's Coacher Federation, told Anadolu. "Another 7,000 to 8,000 buses are also coming to Istanbul districts," he said.

Istanbul residents postponed vacation plans, changed wedding dates and altered summer holidays to be able to vote.

Taxi driver Isa, originally from the southeastern province of Siirt, said a wedding he was due to attend there was brought forward one week so people could get back in time to vote.

"Around 300 of us went to the wedding. We came back so that our right to vote would not go to waste," he said after casting his ballot for the AKP's Yildirim.

"I am relieved that there is a rerun because if there is corruption the vote should be renewed," he said, alluding to the AKP allegations of voting irregularities.

Polling stations in Istanbul closed at 5 pm (1500 GMT) and results were expected later in the evening. (Writing by Humeyra Pamuk; Editing by Jonathan Spicer and Gareth Jones)