Chaos descended on parts of Kenya Wednesday as the first of three days of rallies saw opposition backers clash with police who fired tear gas and live rounds into crowds to thwart the demonstrations over disputed presidential polls.

A sense of normalcy returned to some areas of the capital Nairobi in the morning, with Kenyans heading to work and a free flow of traffic on the streets, but security intensified as the day went on and angry protestors demanded they be allowed to meet at the planned downtown gathering point.

Opposition backers, who charge the presidential polls last month were rigged, were sealed into slums by police, but tried to burst out by throwing rocks and rolling a rusted water tank into the police line.

"I haven't seen anything like this since colonial times," said John Ilidede, 71, in a face-off with police. "There was no democracy then and now there is none either."

The three days of demonstrations kicked off in some of the 25 cities and towns across the East African nation, which descended into violence after last month's polls that swept President Mwai Kibaki back into power in a vote that observers said was flawed.

Protests in the coastal town of Mombasa and the opposition stronghold Kisumu on the shores of Lake Victoria were met by harsh police response as well, as the rallies have been banned by the government.

In Eldoret, the epicentre of violence that was sparked by the polls, local media reported the town centre was empty.

"We are defending our rights. We won't stop until Kibaki steps down and he knows we are angry," said David Odhiambo, a carpenter who lives in Kibera, East Africa's largest slum.

But the momentum of the opposition Orange Democratic Movement (ODM) seemed to be waning slightly Wednesday, with many Kibera residents deciding to stay home or go to work rather than make their way to the downtown park where the Nairobi rally was set to take place.

"We fear for our lives. Mass action doesn't help and only makes problems with police," said Jane Milimu, 40. Some slum dwellers were scorned by their neighbours for heading to work.

Odinga denied that the movement was losing steam, blaming little action in Nairobi on a heavy morning downpour.

"The mass is there. It will continue as we have planned it. There is a heavy presence of police, but people are moving," he said.

Rioting broke out when backers of defeated presidential candidate Raila Odinga tried to reach Uhuru Park for earlier demonstrations as protestors were thwarted by heavily armed riot police who shot tear gas and live ammunition at the crowds.

The unrest brought the thriving capital and other parts of the country to a standstill as stores closed for fear of violence and transport came to a halt.

The violence that was ignited by the elections has seen some 600 people killed and 250,000 uprooted from their homes.

The recent developments in Kenya mark a disturbing change in the usually peaceful country praised as a beacon of stability in a volatile region.

Odinga has pledged to continue mass action despite calls from Kenya's leading newspapers that he take his grievances to parliament, where ODM holds a significant majority over Kibaki's Party of National Unity.

In a boost to Odinga, the first session of parliament held since the polls saw the National Assembly on Tuesday elect his preferred candidate for speaker. Odinga called it a "momentous victory for the people of Kenya."

Some Kenyans said they would not demonstrate because they saw hope in the election of ODM candidate Kenneth Marenda as speaker.

"It shows there is democracy," said Abdul Rahim, 18.