Police and opposition supporters have clashed over the latter defied government ban and took their anti-IEBC demos some city centres.
In Mombasa, anti-riot police were not taking chances as they swarmed the coastal city's streets to enforce the government directive.
They dispersed a group of National Super Alliance (Nasa) supporters who had converged on Uhuru Gardens along Moi Avenue and later Nkrumah Road.
Deputy Governor William Kingi, Senator Mohammed Faki and Mvita MP Abdulswamad Nassir were leading the protests when police fired the corrosive gas.
The protesters and their leaders scampered for safety, with police in hot pursuit.
It was not immediately clear if the officers made any arrests and if the protesters suffered any injuries.
A clash was looming in the capital Nairobi and Kisumu, the other cities the government has banned demos in central business district.
In Kisumu, Orange Democratic Movement, a Nasa affiliate party, said they would enter the CBD of the lakeside city.
Kisumu Senator Fred Outa told the Nation that they would stage demos in all parts of the town.
According to Mr Outa, Interior acting Cabinet Secretary Fred Matiang’i, who banned the demos in CBDs, does not have powers over the Constitution which "guarantees right to picket."
By 9am, protesters had started gathering at Kondele area in readiness for their march to the offices of the Independent Electoral and Boundaries Commission (IEBC) in Milimani.
Police blocked major roads leading to town at the Aga Khan roundabout.
They used teargas to break up an assembly of Nasa supporters around the Aga Khan Hospital and the town’s main stage.
In Nairobi, police tear-gassed Nasa leaders, led by James Orengo, as they left their Upper Hill office to stage anti-IEBC demos in Nairobi CBD.
There was an uneasy calm and normalcy ahead of the planned demos.
But the central business district of the capital was on a police lockdown.
Although a number of businesses were open in midmorning, police officers continued patrols along major streets of the capital.
Uhuru Park, where the demos have been starting, was cordoned off by police to allow military training ahead of the Mashujaa Day celebrations.
The officers, dressed in anti-riot gears, equally sealed off the anniversary towers, which houses the IEBC headquarters.
ODM Chairman John Mbadi told the Nation that he was preparing to lead the demos to the city centre.
He said they do not recognise Dr Matiangi' s directive.
He said they were prepared for anything as they seek to “liberate majority Kenyans from autocratic rule”.
In Migori, Nasa protesters defied local police order and staged demos in the border town’s centre.
The protesters, who have carried placards and twigs, blocked main roads in the town and lit bonfires across the streets.
Homa Bay County Commissioner Kassim Farah warned that the lawlessness would be dealt with decisively.
"We shall not hesitate to deal with protesters who are attacking police officers and destroy other people's properties," said Mr Farah.
A contingent of anti-riot police officers have begun patrolling the streets to battle the protesters who have vowed to march towards Homa Bay Police Station and IEBC offices.
The protesters have forced traders in the town to join them or have their business premises vandalised.
Businesses have closed in the town.
The opposition is pushing for systems and personnel changes at the Independent Electoral and Boundaries Commission (IEBC) before repeat presidential election, including the dropping of Dubai-based ballots printer Al Ghurair and French technology supplier OT-Morpho.
Nasa also wants IEBC CEO Ezra Chiloba and 10 other top officials accused of bungling August 8 poll , which was quashed by the Supreme Court, shown the door.
Reported by Mohamed Ahmed, Justus Ochieng, Barack Oduor, David Mwere and Silas Apollo.