Tens of thousands of people demonstrated in cities across Russia in support of Prime Minister Vladimir Putin on Saturday in a show of force two weeks before a March 4 presidential election that is expected to return him to the Kremlin.

The rallies began in the Pacific coast port of Vladivostok and culminated with a late-night demonstration on wheels in Moscow, where motorists took to the streets with slogans such as Putin rules on their cars.

One wish unites us: we want to be sure of tomorrow, said a declaration read out at the rally in St. Petersburg, which like many others was organised by trade unions that have close government ties.

The declaration urged Russians to vote on March 4 and defend the right to the stable future.

In central Moscow, about 10 people staging a street protest against Putin were detained, Ekho Moskvy radio reported.

The pro-Putin rallies are aimed at showing that the prime minister, who could remain president until 2024 if he wins two straight terms, has majority support despite the biggest opposition protests of his 12-year rule.

Opponents say state workers are pressured to attend the pro-Putin rallies with a combination of threats and payments, and that police exaggerate the size of the crowds while underestimating the size of opposition protests.

Tens of thousands of people have turned out for opposition protests in recent months, venting anger over suspected fraud in December's parliamentary election, and over what they see as a lack of say in Putin's tightly controlled political system.

On February 4, when opponents held their most recent big protests in Moscow, supporters of Putin staged a rally that may have been even bigger and echoed his portrayal of the protesters as Western-funded troublemakers bent on revolution.

At Saturday's rallies, demonstrators said they wanted stability, which Putin says he brought to Russia after the economic troubles ushered in by the 1991 collapse of the Soviet Union.

Authorities said crowds of thousands gathered in many cities, and as many as 60,000 in St. Petersburg, Russia's second city and the hometown of Putin, who was president from 2000-2008 and still, as prime minister, Russia's dominant politician.

In Oryol, a city south of Moscow, demonstrators chanted Russia, Putin, Victory! and vowed to prevent new upheaval.

We have come to this rally today to say that we do have something to defend. We want to say as loudly as possible that we support Vladimir Vladimirovich Putin, youth movement leader Ivan Arkatov told the crowd, according to Itar-Tass.

We stand for the unity of the country and for stability, Itar-Tass quoted a student activist in the Volga River city of Nizhny Novgorod as saying. We are the people of Russia and we will decide Russia's fate.

The pro-Putin car rally in Moscow late on Saturday followed a similar demonstration against Putin, and in favour of fair elections, that was organised by opposition activists on January 29. They plan another car protest on Sunday.

(Writing by Steve Gutterman)