Authorities in the Kenyan capital began enforcing a ban on smoking in public places on Wednesday as Nairobi became the latest world capital to reject its harmful effects.
Smoking has been outlawed in restaurants, bars, offices, public buildings, markets, malls and theatres a year after the Kenyan High Court blocked the measure.
Offenders face fines of up to 3,000 shillings (45 dollars) or six months in prison.
Nairobi mayor Dick Wathika urged bar and restaurant owners to create designated areas for smokers as the ban took effect on Wednesday.
"We will move with speed to enforce the ban ... You will see our officers busy marking areas so that we are able to provide smokers their (smoking) zone," Wathika told reporters.
"You are free to challenge us," in court, he added.
A smoking ban is already in effect in the Rift Valley town of Nakuru and the port city of Mombasa.
Last year, the high court blocked the implementation of a nationwide ban introduced by the government, pending the outcome of a lawsuit filed by Kenya's tobacco growers.
Smoking provides the Kenyan government with around five billion shillings (74.6 million dollars, 55.5 million euros) per year in taxes, but costs five times as much in disease, disability and death, according to official figures.
Kenya is Africa's second country to introduce a partial smoking ban after Tanzania, which banned smoking in many public places in 2003.
Norway, Italy, Ireland and Britain are among a number of European countries to ban smoking in the workplace and confined public spaces like restaurants and bars.