The government's immigration services department said the "maiden visa-free arrivals" landed in Nairobi from Ethiopia's capital Addis Ababa and more were expected to touch down in coming days.
Immigration and Citizen Services Principal Secretary Julius Bitok said visa requirements would be waived for all travellers to Kenya regardless of nationality.
Under the new system, travellers apply online for an electronic travel authorization (ETA)and pay a $30 (about R560) "processing" fee.
"Right now... all countries around the world including Africa, Asia, America, Australia, and all over the world, are able to come in visa-free," he said at the launch of the scheme at Nairobi's Jomo Kenyatta International Airport.
Last year President William Ruto announced that Kenya would become a "visa-free country" and existing requirements would be waived come January.
Even so, as recently as last Tuesday the Kenyan Civil Aviation Authority warned the new ETA system was "in the process of development and implementation."
The number of tourist arrivals in 2022 rose to 1.54 million, still below pre-pandemic levels, according to tourism ministry figures.
Kenya Tourism Board chair Francis Gichaba voiced hope in November that the figure could top two million in the latest financial year, surpassing the 2019 figure of 1.9 million.