Police officers have dispersed youths who were converging at Jacaranda Grounds in Nairobi, one of the starting points for the Opposition demonstrations in the city.
Officers fired tear gas canisters at youth who were assembling in small groups in readiness for the protests.
There is a heavy presence of police officers at all corners of the venue.
The officers arrested several youths who were bundled into waiting vehicles and taken away.
Opposition Chief Raila Odinga said the anti-government demonstrations will go on for three days this week.
He said the demos will be held whether the government issues a permit or not.
Azimio la Umoja said due to requests from all sectors, the peaceful demos will be held on Wednesday, Thursday, and Friday.
However, President William Ruto said he would use all means to stop the protests.