A Russian court on Thursday granted bail to the last of 30 Greenpeace crew members detained since their September protest against Arctic oil drilling.

The decision to free the ship's Australian radio operator Colin Russell reversed an earlier ruling and is likely to take diplomatic pressure off Russia as it prepares to host the upcoming Winter Olympic Games.

Russell was the only member of the multinational Arctic Sunrise crew to have had his bail request denied in a series of hearings held since November 18.

"Excellent news! Colin Russell from Australia is granted bail," the global environmental protection group tweeted in a message moments after a court in Saint Petersburg issued its ruling.

State television showed the 59-year-old Australian delivering court testimony by video link from behind heavy metal bars of a dark jail cell in his Saint Petersburg detention centre.

The campaigners' open-sea protest targeted what will be Russia's first operational oil rig in the Arctic -- a politically sensitive region that President Vladimir Putin views as the future of the country's energy exporting might.

Irate Russian authorities initially accused the crew -- two of whose members unsuccessfully attempted to scale the platform -- of piracy before reclassifying the offence to the less serious charge of hooliganism.

Thursday's ruling came less than two week after the same court ordered that Russell remain in pre-trial detention until the day after Russia's Winter Games end in the Black Sea resort of Sochi on February 23.

That decision sparked concern that Russia intended to ignore mounting international pressure and take a tough line with the other members of the mostly foreign crew.

Officials never explained their apparent change of heart. But some analysts speculated that Russell's initial bail hearing was held before judges had received Kremlin instructions to go easy on the crew in the face of the developing diplomatic scandal.

The Saint Petersburg court's decision was met with relief by Russell's family and a stern determination to keep fighting the charges by Greenpeace itself.

"I am so relieved that my beautiful, peaceful man will soon be out of detention," Russell's wife Christine said in a statement released by Greenpeace.

"It remains a really difficult time and only when all of the Arctic 30 are free to go home will we be able to properly celebrate," she added.

Australia's Ambassador Paul Myler also tweeted a message saying he was "very happy".

The icebreaker's crew comprised nationals from 18 countries besides Russia and it remains unclear when the foreigners will be allowed to go home.

The hooliganism charges the crew still face carry seven-year sentences and the whole crew has been forced to stay in a Saint Petersburg hotel pending trial -- should one still take place.

Kremlin chief of staff Sergei Ivanov said on Saturday that the foreigners may actually be allowed to leave the country "as soon as the issue of how they can leave Russia is resolved".

State media said the problem hindering the crew members' departure appears to be their lack of Russian visas.

"This is not over yet," said Greenpeace campaigner campaigner Ben Ayliffe.

"Charging them with hooliganism is both an insult and an outrage and none of us will truly be celebrating until they have been allowed to return home and the charges against them have been dropped."

Greenpeace said Russell would be released from prison as soon as the Saint Petersburg court accepts the organisation's two-million-ruble ($60,000) bail payment.

The Kremlin last week rejected a separate decision by an international maritime tribunal in Germany for Russia to return the Dutch-flagged icebreaker to Greenpeace.