The death toll in the collapse of a six-storey building in Nairobi rose to 21 on Monday after four more bodies were pulled from the rubble of the residential structure that gave way during weekend storms.

"As of today we have 21 people dead so far after four bodies were retrieved in the night and another died in hospital," the head of the National Disaster Management Unit, Pius Masai, told reporters, revising a previous count of 16 dead.

Authorities had previously put the number of deaths in Friday's collapse of the building in the low-income district of Huruma at 16.

But the Kenya Red Cross said 60 people were still missing, meaning the final toll could be much higher, although it was unclear whether those sought were at home when the building buckled.

The building, which was home to more than 150 families, many of them living crammed into a single room, had been earmarked for demolition after being declared structurally unsound.

But an order by building authorities for the evacuation of the bloc, built only two years ago near a river, went ignored.

On Saturday, President Uhuru Kenyatta called for the building's owner to be arrested,

A day later, the owner turned himself over to police.

Several buildings have collapsed in recent years in Nairobi and other Kenyan cities, where a property boom has seen buildings shoot up at speed, often with scant regard for building regulations.

The deaths in Huruma bring to at least 28 the number of people who died in Nairobi since the weekend in accidents linked to floods caused by torrential rains.