Thousands of supporters of Alexei Navalny took to the streets of Moscow on Wednesday to protest his detention and back calls for the hunger-striking Kremlin critic to be given proper medical care.

Defying warnings and a massive police presence, the protesters in Moscow marched through the city centre near the Kremlin chanting "Freedom" and "Putin is a thief!", just hours after President Vladimir Putin delivered his annual state of the nation address.

Opposition supporters rallied in Moscow chating 'Freedom!'
Opposition supporters rallied in Moscow chating 'Freedom!' AFP / NATALIA KOLESNIKOVA

Though large crowds assembled, the protests were not on the scale of pro-Navalny demonstrations seen earlier this year, when tens of thousands rallied and thousands were arrested.

Police said 6,000 people had gathered in Moscow.

"This is a fight for the future, we don't have any here," 51-year-old protester Andrei Zamyatin told AFP in central Moscow.

Police arrested more than 1,000 people across Russia, a monitoring group said
Police arrested more than 1,000 people across Russia, a monitoring group said AFP / Olga MALTSEVA

"Navalny is trying to change the system and is being punished for it."

In Russia's second city Saint Petersburg some 4,500 protesters gathered, police said.

IMAGES Thousands of supporters of Alexei Navalny take to the streets of Moscow to protest his detention and back calls for the hunger-striking Kremlin critic to be given proper medical care. Defying warnings and a huge police presence, the protesters in M
IMAGES Thousands of supporters of Alexei Navalny take to the streets of Moscow to protest his detention and back calls for the hunger-striking Kremlin critic to be given proper medical care. Defying warnings and a huge police presence, the protesters in Moscow march through the city centre near the Kremlin chanting "Freedom", just hours after President Vladimir Putin delivered his annual state of the nation address. AFPTV / Andrey BORODULIN

In the central city of Vladimir -- which is home to a prison where Navalny is currently being kept under medical observation -- some 200 people rallied, an AFP correspondent reported.

Protesters marched through the city centre while police urged people to disperse.

Thousands gathered in second city St Petersburg whre Russian riot police blocked off a street
Thousands gathered in second city St Petersburg whre Russian riot police blocked off a street AFP / Olga MALTSEVA

Maria Taikova, a 60-year-old protester in Vladimir, said police were restrained because Wednesday's protests might have been Russia's last for years to come as prosecutors seek to outlaw Navalny's Anti-Corruption Foundation.

"It will be labelled 'extremist' and we will all be jailed," she told AFP.

Demonstrations earlier took place in other cities including Vladivostok in the Far East, and Novosibirsk, Irkutsk and Tomsk in Siberia, with police saying more than 14,000 people had protested in 29 cities.

Police had issued a warning against taking part in "illegal gatherings" and detained more than 1,000 people across the country, according to monitoring group OVD-Info.

Navalny ally Lyubov Sobol and his spokeswoman Kira Yarmysh were detained ahead of the protest.

The protesters are demanding that Navalny, who launched a hunger strike three weeks ago, be freed or at least given proper medical treatment after his doctors said his health was failing and he could die "at any minute".

Those taking part said they believed it was important to join the demonstrations, but few expected the Kremlin to listen.

"I don't think this protest can save Navalny. There would need to be at least 200,000 to 300,000 people in the streets," said protester Alexander Butuzov, 51.

Navalny was arrested when he returned to Russia in January after months recovering in Germany from a near-fatal nerve agent poisoning he blames on the Kremlin -- an accusation it rejects.

He was sentenced to two-and-a-half years on old fraud charges his supporters say were politically motivated and has been serving time in a penal colony about 100 kilometres (60 miles) east of Moscow.