* Opinion polls give Putin around 70 percent support
* He's on course for second consecutive term
* With little real contest, turnout may be low
* Kremlin critics allege turnout artificially inflated (Updates throughout with new quotes, details)
UST-DJEGUTA, Russia, March 18 (Reuters) - Russians vote in a presidential election on Sunday expected to give Vladimir Putin an easy victory, though the Kremlin could miss out on the resounding mandate it wants if large numbers, bored by a one-sided contest, do not bother to vote.
Opinion polls give Putin, the incumbent, support of around 70 percent, or nearly 10 times the backing of his nearest challenger.
Another term will take him to nearly a quarter century in power a longevity among Kremlin leaders second only to Soviet dictator Josef Stalin.
Many voters credit Putin, a 65-year-old former KGB spy, with standing up for Russia's interests in what they view as a hostile outside world.
A row with Britain over allegations the Kremlin used a nerve toxin to poison a Russian double agent in a sleepy English town denied by Moscow has not dented his standing.
"I voted for our liberator, Putin," said Alexander Kiryukhin, a 79-year-old in the city of Simferopol, Crimea. Russia's annexation of the region from Ukraine in 2014 earned Putin condemnation from Western governments and admiration from many Russians.
"He sorted our lives out, he's irreplaceable for the state," said Kiryukhin.
Putin's opponents alleged officials were trying to inflate the turnout, by opening up stalls selling discounted goods at polling stations, and instructing state employees to report back to their bosses that they had voted.
Reuters reporters witnessed multiple people in different locations voting in groups, and then taking photos of themselves in front of the ballot boxes on their mobile phones.
In polling station 1515 in Zelenodolsk, 800 km (500 miles) east of Moscow, five people photographed themselves voting. Asked by a Reuters reporter why, one of the group, a young woman, said: "What do you mean why? It's a photographic report for our bosses."
At polling station number 216 in Ust-Djeguta, in the Karachayevo-Cherkessia region of southern Russia, Marina Kostina was marshalling groups of voters to be photographed. Asked why one woman was photographed, Kostina said: "Her work asked her to report in."
The first politician in years to challenge the Kremlin's grip on power, Alexei Navalny, is barred from the race because of a corruption conviction he says was fabricated by the Kremlin. He is calling for a boycott of the election, saying it is an undemocratic farce.
A day of voting across Russia's 11 time zones began at 2000 GMT on Saturday on Russia's eastern edge, in the Pacific coast city of Petropavlovsk-Kamchatsky. Voting will run until polls close at the westernmost point of Russia, the Kaliningrad region on the Baltic Sea, at 1800 GMT on Sunday.
The majority of voters see no viable alternative to Putin: he has total dominance of the political scene and state-run television, where most people get their news, gives lavish coverage of Putin and little airtime to his rivals.
Many Russians believe he has restored stability after the chaos that ensued after the Soviet Union collapsed.
A March 9 survey by state-run pollster VTsIOM gave Putin, who was first elected president in 2000, support of 69 percent. His nearest rival Pavel Grudinin, the Communist Party's candidate, was on just 7 percent.
"There is no intrigue. I do not see any point for me in going to the election," said Alexei Khvorostov, a resident of Krasnodar, in southern Russia.
Ella Pamfilova, head of the commission organising the vote nationwide, has said any fraud will be stamped out.
She said those alleging the election was rigged were biased and peddling "Russophobia", echoing a line used by the Kremlin to describe Western criticism of Russia.
A low turnout would diminish Putin's authority in his next term, which, under the constitution, has to be his last.
Yevgeny Roizman, a Kremlin opponent who is mayor of the industrial city of Yekaterinburg, said officials were using inducements to persuade people to vote.
"They're herding the whole country to the polling stations," Roizman, a rare example of an elected official opposed to the Kremlin, said in a video blog. "It's degrading... We're not sheep."
Irina Kornienko, 68, was running a stall selling clothes at a school in Kemerovo, Siberia, that was hosting two polling stations. Her T-shirts were on sale for 200 roubles ($3.48), and underwear for 50 roubles.
She said she was given special incentives by the local government to set up her stall on Sunday.
"The administration told me I could sell my stuff at a lower price if I came here today. These prices aren't usually allowed. It's the same for the people selling food, the prices are much lower. But thats good for people here, life is hard," she said.
($1 = 57.5056 roubles) (Additional reporting by Reuters reporters; writing by Christian Lowe; editing by Jason Neely)