The crowds started to form before dawn in Kibera, one of Africa's largest slums and the stronghold of opposition leader Raila Odinga.

The poll was due to open at 5am, but the doors of the polling station in Kibera Primary School remained shut as more and more people arrived from the maze of potholed tracks and ramshackle dwellings.

Frustration mounted as the numbers grew, and the air of chaos did not lessen when the doors finally opened before 9am, with voters uncertain where to go and which door to use.

Inside there was confusion. Some of the registrar's list of registered voters appeared to be missing. There were allegations that all the lists containing surnames beginning with "O" had gone missing. This was a serious allegation, because Mr Odinga belongs to and draws his support from the large Luo tribe, and almost everyone in Kenya whose surname begins with an "O" is a member of the Luo.

Mr Odinga himself claimed that the list with his name on it was missing and that he was unable to vote. But a reporter from the Associated Press reporting seeing Mr Odinga's name on a register in the polling station, which suggests that the missing lists may merely have been mislaid. Other reports suggested that the lists had not been in place when the polls were due to open but arrived later in the morning.

The head of the European Union observer mission said that incompetence appeared to be to blame rather than corruption, as a register was also apparently missing of voters whose name began with "M" — almost all of them members of the president's Kikuyu tribe.

The voters at Kibera started to accuse President Mwai Kibaki's party of trying to rig the vote. The suspicion was that his supporters had stolen the Luo lists. The crowds started banging to get in, fighting their way through the door and demanding to vote. Young men were smashing windows. Police declined to intervene.

Brenda Odul, a voter in the queue at Kibera, told me that instigators in the crowd seemed to be trying to foment violence, urging people to torch the polling station. Frightened by the violent atmosphere, a number of voters started to drift home.

"It's very sinister," said Mrs Odul. "In other polling stations around the country things were going smoothly. I think it is very odd because there have been plans for this vote for a very long time, but still this happened. The police said there's nothing we can do and the officials weren't explaining anything. At one point they just shut the door."

It was at this moment that volunteers emerged from the crowd and took matters into their own hands. They persuaded people to form a queue and shouted for the women to vote first and then return to the safety of their homes.

"Things got a lot better after some people volunteered to organise the whole situation," said Mrs Odul.

Mr Odinga returned to the polling station, and this time he succeeded in voting, she added.

The polls were expected to close at 5pm, but organisers announced that they would stay open as long as necessary for everyone in line to vote. This defused the situation, although it remains to be seen whether the people who were scared off earlier came back and voted. If not, there may be accusations that they were denied their right to vote.

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