National Super Alliance (Nasa) leader Raila Odinga is back in the country after 10-day trip in the US.
The plane carrying Mr Odinga and his daughter Winnie landed at the Jomo Kenyatta International Airport in the capital Nairobi at 11.13am.
Mr Odinga did not go through the VIP lounge as most leaders do. Instead, he left the airport through Terminal 1C like any other traveller.
The plane touched down as police engaged his supporters, who wanted to force their way into the heavily guarded airport, in running battles.
Some 200 supporters, including women, beat the security cordon and entered the airport.
They waited and received Mr Odinga inside the airport with their signature rendition of "Raila Tibim", "Raila Tialala".
Nasa leaders who received Mr Odinga at the airport included Kisumu Governor Anyang' Nyong'o, MPs Ledama ole Kina, Otiende Amollo, Babu Owino, Opiyo Wandayi, Godfrey Osotsi, Rose Nyamunga and his former Legal Adviser Miguna Miguna.
His convoy is now heading to Nairobi's Central Business District as he moves to Uhuru Park where he is expected to address a rally.
Hundreds of his supporters, the majority on foot, are accompanying him and police are having a rough time controlling traffic on Mombasa Road.
Earlier, the Nasa supporters clashed with police as they attempted to force their way into the airport.
Inspector-General of Police Joseph Boinnet and Nairobi County Commander Japhet Koome had outlawed the Nasa supporters' assembly at the airport citing security concerns.
But in defiance, hundreds of youths had started arriving at the airport as early as 8am in what Nasa leaders had described as “a million march” to receive Mr Odinga
Police had thrown heavy security cordon along Mombasa Road to stop the youth and other Nasa supporters from accessing the airport
Entry to the airport was tightly controlled and all motorists entering the facility had to be searched and screened.
At one point, police were forced to rush to City Cabanas to stop about 300 youths who were marching to the airport.
In the ensuing melee, Rarieda MP Otiende Amollo had one of the windows of his car smashed by stones as the youths fought off the police.