NAIROBI, Jan 30 (Reuters) - Kenyan authorities shut down television and radio stations on Tuesday as supporters of opposition leader Raila Odinga watched him take a symbolic presidential oath on the Bible in a Nairobi park in a direct challenge to President Uhuru Kenyatta.Odinga's supporters insist that he, not Kenyatta, is Kenya's legitimate leader, and that Kenyatta's election was neither free nor fair.Kenyatta's election victory in August was annulled by the Supreme Court over irregularities, but he then won a re-run, which Odinga boycotted over a failure to revamp the electoral commission, and was sworn in for a second term in November."I, Raila Omolo Odinga, do swear that I will protect the nation as people's president, so help me God," Odinga said to the cheers of more than 10,000 people in Uhuru Park, near Nairobi's main business district.The attorney-general had warned that Odinga could be charged with treason if the event went ahead - an offense that can carry the death penalty.As people assembled, authorities had begun to force independent television and radio stations reporting on the gathering off air, several outlets said - the most widespread censorship for a decade."We have an illegitimate government which is pretending to be in power," Odinga told a local broadcaster by phone in an interview that was streamed online. "Whenever there is a crisis, there is also an opportunity. This is an opportunity to bring the country together." Odinga refused to be drawn on his plans for after his symbolic inauguration, repeatedly telling the interviewer, "Hold your horses" and "We'll see."Many of the protesters were chanting pro-Odinga slogans, waving tree branches and blowing horns and whistles."Odinga is the one we recognize as the president and that is why we are swearing him in," said hairdresser Benta Akinyi, 32.Many of those at the rally had come from the capital's slums. Odinga has strong support there, and in the west and along the coast, areas where people have long felt ignored by central government and shut out of political patronage networks.PREVENTABLE CRISIS"This is a lose-lose situation for both Kenyatta and Odinga and it was an entirely preventable crisis. It's not clear where Odinga goes next from here," said Murithi Mutiga, a senior analyst for the International Crisis Group."Kenyatta as well - by resisting all attempts at dialog, he has put himself in a position where he will continue to struggle to be seen as the president of all Kenyans."Although the police had said they would prevent any illegal assembly, there were no uniformed police in the park and no anti-riot officers or vehicles were visible. On the edge of the crowd, a single tear gas canister was fired. Nearly 100 people were killed over the prolonged election period, mostly in clashes between Odinga supporters and police.The local radio station Capital FM reported that Odinga's supporters had been granted permission to use the park, but police and government spokespeople could not be reached for comment."We intend to hold a peaceful event," Odinga's NASA alliance said in a statement late on Monday."We nonetheless wish to put the (ruling party) Jubilee administration on notice that we will accomplish our mission, come hell or high water. We advise our supporters to come prepared to stay until our mission is accomplished."By 10:20 a.m. (0720 GMT), a number of independently owned media outlets including Citizen radio and television, NTV and KTN said that authorities had forced them off air."The Communications Authority of Kenya has switched off Citizen Television and Radio in most parts of the country over the coverage of the NASA 'swearing-in' plan," Citizen said on its website.A Communications Authority spokeswoman said it would comment later.On Monday, Linus Kaikai, chairman of the Kenya Editors' Guild, said editors had been warned by the authorities that they could be shut down if they covered the event.