Kenyan authorities have shut down TV stations to prevent live coverage of a swearing-in ceremony by opposition leader Raila Odinga who lost last year's disputed presidential election.
Several hundred supporters are gathering at a park in central Nairobi, where the event is being held.
The result of the August general election was annulled following allegations of irregularities.
Uhuru Kenyatta won a repeat election in October, boycotted by Mr Odinga.
The president warned the media not to cover Tuesday's event and the attorney general said holding it amounted to treason.
How did the TV ban take hold?
Two privately owned television stations - NTV and Citizen TV - were observed to go off air from around 09:10 (06:10 GMT), BBC Monitoring reports.
Citizen TV told the BBC the government authorities had forced them off the air over plans to cover the gathering.
It is unusual to actually switch off the broadcasting signals of media houses in Kenya, the BBC's Anne Soy reports from Nairobi.
Threats have been made in the past and some media houses have been raided but none has actually had their signal deliberately disrupted, our correspondent says.
Some schools are closed in the Kenyan capital because of the event, and people do not know what to expect, our correspondent says, adding there is tension in the country.
Police had cordoned off the park earlier, but then withdrew, she says.