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 elections.
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.
What do Odinga supporters say?
One of them, Larry Oyugi, said there was nothing illegal about Tuesday's event: "We have warned the police enough and we are also going as per the constitution. The constitution of Kenya, article one, allows all Kenyans to exercise their power directly.
"This is why we are here to exercise our powers by gathering here and also article 37 allows peaceful assembly. We are citizens of this country, we are allowed to peacefully assemble here and elect our president as per the constitution."
Why is the election result disputed?
Mr Kenyatta was officially re-elected with 98% of the vote on 26 October but just under 39% of voters turned out. He was inaugurated in November.
His victory is not recognised by Mr Odinga because he says he was elected by a small section of the country.
Mr Kenyatta also won the original election on 8 August but that result was annulled by the Supreme Court, which described it as "neither transparent nor verifiable".
When the repeat vote was called, Mr Odinga urged his supporters to shun it because he said no reforms had been made to the electoral commission.
Correspondents say the election dispute has left Kenya deeply divided. About 50 people are reported to have been killed in violence since the August ballot.
However, A section of the youth attending the National Super Alliance (NASA) ‘swearing-in’ at Uhuru Park has destroyed the banner at General Post Office (GPO) roundabout along Uhuru Highway and Kenyatta Avenue.
The rowdy crowd of about 20 men climbed the billboard, destroying part of it before carrying the court of arms into Uhuru Park.
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Erected in towards in November 2017 by Nairobi County government, the billboard had Uhuru Kenyatta’s name as the President of the Republic of Kenya, the court of arms and Nairobi County government seal.
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