One survivor was pulled from the huge pile of debris shortly after dawn, Kenya Red Cross said, some 10 hours after the building collapsed on Friday night and as skies cleared after a night of ferocious storms.

"We have lost seven people after the house collapsed last night," Nairobi police chief Japheth Koome told AFP. "We have 121 others who have been rescued and taken to hospital."

Kenya Red Cross, who along with police and other rescue services continued to search the piles of crumbled concrete rubble, said a total of 150 households had been affected.

Two neighbouring buildings in the densely-populated and poor Huruma neighbourhood were declared unsafe on Saturday and are being evacuated.

In other separate incidents, two people drowned when their vehicle was swept away by storm waters in the capital's Industrial Area, another person died in floods, and four were killed when a wall collapsed, Koome added.

Nairobi Deputy Governor Jonathan Mueke, who visited the scene of the destroyed building on Saturday morning, said an investigation would look into why the two-year old building had collapsed.

"The building went down during the heavy rains, but we still want to establish if all the procedures were followed when it was constructed," he said.

The building collapsed at around 9:30 pm Friday following some of the heaviest downpours since the start of the rainy season.

They have caused flooding and landslides in many areas of the city. Kenya Red Cross spokeswoman Arnolda Shiundu said the site had been "complete chaos" and teams were "still searching," assisted by a crane.

"We don't know how many people are under the rubble, but we fear there are still several of them," she said.

Pictures broadcast by local media showed soldiers, policemen and civilians searching through the rubble of the collapsed buildings for survivors.

Nairobi has been in the middle of a building boom for some years but the quality of materials used and speed of construction have sometimes been called into question.

The growing middle class has triggered an explosion in demand for housing and a rise in real estate prices in the east African capital.