police have fired tear gas at crowds gathered at Kamukunji grounds in the capital, Nairobi, where opposition veteran Raila Odinga was expected to address his supporters.
Livestreamed video at the grounds shows stage technicians scrambling for their equipment.
A section of the multimillion-dollar Nairobi expressway has been closed due to the demonstrations, its management company says.
Videos on social media appear to show a group of people vandalising the road.