Russian opposition leader Alexei Navalny has arrived at a Berlin hospital for treatment after collapsing on a plane on Thursday.

Navalny's allies claimed that his tea had been laced with poison, although his doctor said that no poison was found in his body following medical tests on Friday.

Navalny arrived in Germany's capital from the Russian city of Omsk via air ambulance on Saturday morning before being rushed to hospital in a convoy of ambulance and police vehicles. 

Read more: Russian opposition leader Navalny in coma – allegedly poisoned by tea

Berlin's Charite hospital complex said they would begin treatment of Navalny with "extensive" diagnostic tests.

"After completing the examinations and after consulting the family, the physicians will comment on the disease and further treatment steps," the hospital said. "The examinations will take some time."

Before Navalny flew from Omsk to Berlin, hospital staff in Russia said that his life was not in immediate danger and that he was in an induced coma. 

The Cinema for Peace Foundation, who arranged to send the air ambulance for Navalny has since said that the opposition leader's condition was stable.