An ambulance on Saturday took Russian opposition leader Alexei Navalny from the hospital where he was being treated in the city of Omsk to the airport for medical evacuation, his spokeswoman said.
"Alexei Navalny has been loaded into an ambulance and they are taking him to the airport," his spokeswoman Kira Yarmysh tweeted.
An AFP journalist saw the ambulance arrive at the airport.
A private plane chartered by German NGO Cinema for Peace was set to fly Navalny to Berlin's Charite hospital for treatment.
Navalny fell ill on Thursday morning on a plane to Moscow from the Siberian city of Tomsk and it had to make an emergency landing.
Doctors said he was in a coma on a ventilator in a grave state.
His aides say that he was poisoned, apparently with a cup of tea at Tomsk airport.
Russian doctors have denied finding any trace of poison and said Navalny appeared to have a "metabolic disorder" and had suffered low blood sugar.
The air ambulance arrived in Omsk on Friday morning but Russian doctors said that Navalny was too unstable to be moved.
They announced on Friday evening that they had agreed to let him be transferred after German doctors examined him and Navalny's wife Yulia appealed to Russian President Vladimir Putin to allow his evacuation.