Nasa supporters on Tuesday began trooping into Uhuru Park as early as 5am ahead of leader Raila Odinga's planned swearing-in.
Nasa CEO Norman Magaya on Monday said attendees should be seated by 8.30am as the ceremony should be over by 1pm.
According to residents, several Nasa MPs, including Dagoretti North MP Simba Arati, were among leaders who had been mobilising supporters from Monday.
Police water cannons started arriving at the CBD by 5am, but they were parked a distance from Uhuru Park.
There was no police presence inside the park early in the morning.
By 7am, a crowd of supporters were singing songs of joy, as they expressed hope that the day would be a success.
Some supporters carried Bibles, saying they were ready to swear in Mr Odinga.
At 8am, police began entering the park.
Nasa supporters gathered near the dais, while a few others were scattered around the park.
But by 8.30am, the few police officers inside Uhuru Park as more Nasa supporters trooped in.
Additional reporting by Samwel Owino.