"They made bonfires out of old tires," the witness said, "and blocked the road. Police finally moved in and fired tear gas at the crowds in order to get them to disperse."
Similar scenes convulsed western Kenya today, where police moved in to quell violent protests.
In the Rift Valley, about 5,000 people set fire to homes and smashed shop windows in Naivasha, dragging away goods.
A police helicopter and two military helicopters then flew over the crowd and officers began shooting, sending people running in panic.
Witnesses reported seeing helicopters swoop down, with officers firing on a mob of armed Kikuyus who were pinning down hundreds of Luos outside the Naivasha Country Club.
Kikuyus, armed with machetes and clubs inset with nails, had prevented the Luos from escaping for two days.
The Rift Valley has seen some of the worst of the post-election violence. At least 90 people were killed there over the weekend. Dana Hughes contributed to this report.