Three people were shot as police officers battled National Super Alliance (NASA) supporters in Nairobi on Friday.
Reports indicate that at least one of them has since succumbed to injuries.
A police lorry was also burnt as the supporters objected to the officers' refusal to grant them access to the city center.
Police are currently using water cannons to disperse NASA supporters on Haile Sellasie Avenue.
The officers could be heard firing bullets as NASA leader Raila Odinga's convoy made its way to Landhies Road in Nairobi.
NASA supporters had gathered to welcome Mr Odinga from the Jomo Kenyatta International Airport (JKIA) where he landed following a 10-day trip to the US and the UK.
There was a heavy police presence along Mombasa Road as many supporters lined up to welcome Odinga.
A major rally had been planned by NASA once Mr Odinga was in the country.
Uhuru Park had been sealed off by police officers but the thousands of supporters have managed to gain access to the area.
Mr Odinga's convoy is still on the move with the venue for the final rally yet to be confirmed.