Moscow, Russia: Authorities detained Russian opposition politician Alexei Navalny and nearly 1,000 of his supporters on Monday, as they mounted demonstrations across the nation against government corruption.

The protests are the second mass action since March called by Navalny, who has announced his intention to run for president next year and has drawn a new generation to the streets through a relentless online campaign.

At least 600 people were detained in Moscow -- where riot police tried to push the crowds back sometimes by beating them with batons -- and 300 in Saint Petersburg, according to an NGO that tracks arrests, with Navalny himself picked up by police as he was headed to the event.

The specialised NGO, OVD-Info, had previously reported detentions in Vladivostock, Kaliningrad, Norilsk and Sochi.

On central Moscow's Tverskaya Street, a helicopter hovered overhead as riot police lined up and pushed back against the crowd, grabbing people and leading them to police vans as others shouted "Shame!", "Putin is a thief!" and "Freedom to Navalny!"

The action also drew thousands to the streets in cities across Russia, with authorities sanctioning some gatherings and banning others. Some reports said authorities threatened university students with expulsion if they attended.

The 41-year-old Navalny's anti-corruption videos have needled the country's most powerful and drawn to the streets crowds unseen since a wave of protests against President Vladimir Putin's reelection for a third term in 2012.

- 'Mired in corruption' -

Navalny, who plans to stand against Putin in presidential elections in March, faces up to 30 days in administrative custody for breaking rules on organising demonstrations, according to his lawyer.

The recent rallies were galvanised by a film released by Navalny in early March which accused Prime Minister Dmitry Medvedev of controling vast personal wealth through a shadowy network of foundations, which has since been viewed over 22 million times.

"Putin has been in power for 17 years and is not planning to leave. He has usurped all power," said protester Alexander Tyurin, 41. 

"Corruption is a system. I work in a construction company and everything is mired in corruption."

Another protester Yevgeny, 19, said he was expelled from university after participating in a previous rally. 

"Our government shouts that enemies are everywhere and is becoming closed in on itself," he said. 

"We want turnover among those in power. Pressure on young people has increased." 

Navalny has brought a new generation to the streets through his embrace of YouTube, and his team was broadcasting from a studio set up in Moscow, though the electricity was periodically cut forcing the presenter to speak in total darkness.

The head of Navalny's anti-corruption group FBK, Roman Rubanov, was detained by police who came to his house, arrest tracking group OVD-Info said.

Moscow police said Navalny would be charged with administrative offences of resisting arrest and a second violation of demonstration organisation rules.

- Russia Day -

The wave of protests called by Navalny coincides with a public holiday, Russia Day, with Putin handing out awards and holding a reception in the Kremlin. 

Turnout was difficult to calculate as ordinary people mingled with those protesting, but thousands filled the Tverskaya Street area in Moscow, many waving Russian flags and banners.

On the eve of the event -- which was authorised -- Navalny announced the protest was changing location to Tverskaya because authorities blocked his efforts set up a stage and sound equipment.

Authorities "are forbidding any contractors from getting us a stage and sound," he wrote on his blog Sunday. 

"We are cancelling the rally on Sakharov Avenue and moving it to Tverskaya Street," a main thoroughfare to the Kremlin, he said.

Moscow City Hall labelled the decision a "provocation" while the police warned that "any provocative actions by the protesters will be viewed as threat to public order and immediately thwarted".

The protest eventually coincided with events held by the City Hall for Russia Day like the reenactment of various eras in Russian history, from World War I trenches to a Renaissance fair and sword fighting.

In surreal scenes, dozens of buses filled by policemen were parked nearby ahead of the rally while ordinary people gawked at actors in period costumes.

Later, however, riot police and the national guard moved in even on people sitting in nearby cafes, shouting "Go away! There is an unauthorised protest here!"