肯尼亚正进行关键性总统大选
Kenyans are voting in an election that observers describe as the most important in the country's history.
肯尼亚国内正在进行选举投票，观察员称这是该国历史上最重要的一次大选。
Queues grew quickly outside polling stations, like here in Gatundu
It is the first time a vote has taken place under a new constitution, designed to prevent a repeat of violence that followed the 2007 polls.
More than 1,000 people died when supporters of rival candidates clashed over a contested result.
Despite appeals for calm, reports say at least four police officers died in clashes near Mombasa early on Monday.
Officials said a gang attacked police in the region of Changamwe outside the port city in the early hours.
Eyes on the presidency
Kenyans will choose a president, members of parliament and senators, county governors and members of the newly-formed county assembly.
However, the BBC's Gabriel Gatehouse in the capital Nairobi says all eyes are on the presidency.
Eight candidates are standing but it is essentially a two-horse race pitting Prime Minister Raila Odinga against Deputy Prime Minister Uhuru Kenyatta, he says.
Mr Kenyatta, son of Kenya's founding father Jomo Kenyatta, is due to stand trial at the International Criminal Court for his alleged role in orchestrating the violence five years ago.
Mr Kenyatta's running mate, William Ruto, has also been indicted by the court. Both men deny any wrongdoing.
The post-election violence of 2007-8 broke out after Mr Odinga claimed he had been cheated of victory by supporters of President Kibaki.
Supporters of the rival candidates, from different ethnic groups, took up arms against each other.
Mr Odinga later joined a government of national unity under a peace deal.
Our correspondent says long queues formed outside polling stations in Nairobi hours before polls opened.
The atmosphere was calm, he said, and people chanted "peace".