Alexey Navalny in stable condition as he receives treatment in Germany

Russian opposition leader Alexey Navalny is at Berlin's Charite hospital receiving treatment as is in stable condition.

The air ambulance landed at 0647 GMT on Saturday at the military wing of Tegel airport after a day-long standoff over his medical evacuation.

Navalny is currently in a coma after allegedly being poisoned.

Jaka Bizilj, the head of the Cinema for Peace NGO that facilitated his evacuation said Navalny's condition remained stable during the five-hour flight. 

The opposition figure was rushed to Germany for treatment following a day-long standoff over his evacuation from a Siberian hospital.

The 44-year-old lawyer and anti-corruption campaigner, one of President Vladimir Putin's fiercest critics, fell into a coma after becoming suddenly ill on Thursday morning on a plane en route to Moscow that had to make an emergency landing in Siberia's Omsk.

His aides claim he was poisoned, allegedly by a cup of tea at the airport, and blamed Putin, though Russian doctors said tests showed no trace of any poison.

READ MORE: Russian medics agree to Navalny's evacuation to Germany

Doctors treating him in Omsk had refused to let Navalny leave on the grounds that he was too unstable to move, but reversed course after his family and staff demanded he be allowed to travel to Germany for treatment.

Poisoned?

Russian doctors initially said he was in a coma on a ventilator in a grave state. 

They added that Navalny appeared to have a "metabolic disorder" and had suffered low blood sugar.

But the regional interior ministry said police detected an industrial chemical after swabbing Navalny and his luggage, although doctors said this would not have caused his condition.

Doctors announced on Friday evening that they had agreed to allow him to be transferred after German doctors examined him and the Cinema for Peace foundation said they were "willing and able" to transport him to Berlin.

The turnaround also followed a letter from Navalny's wife, Yulia, with a direct appeal to Putin and after aides asked the European Court of Human Rights to intervene with the Russian government.

Navalny is the latest in a long line of Kremlin critics who have fallen seriously ill or died in apparent poisonings.

His wife told journalists that she wanted Navalny to be "in an independent hospital, whose doctors we trust".

READ MORE: Who is Alexei Navalny — Russian dissenter and Putin's foe?

Yulia also claimed Russia's refusal to evacuate her husband was a ploy to "play for time" and make it impossible to trace poison, posing a "critical threat to his life".

Navalny has made many enemies with his anti-corruption investigations, which often reveal the lavish lifestyles of Russia's elite and attract millions of views online.

READ MORE: Massive anti-Kremlin protests grip Russia's Far East