Nairobi  - The number of confirmed dead from a building collapse near the Kenyan capital Nairobi has risen to 11, with 30 people still missing, the Kenyan Red Cross said Tuesday.

A five-storey building under construction in the town of Kiambu collapsed on Monday, trapping dozens of construction workers inside.

"Rescue workers at the collapsed building ... have recovered 11 bodies from the rubble," the Red Cross said in a statement on its website.

"The Society has registered 30 missing persons, according to the names presented by relatives and friends."

Some of those trapped have been in contact with friends and relatives via mobile phones, raising hopes that more people could be found alive.

At least 18 people have been pulled from the ruins and taken to hospital for treatment.

Witnesses said a crack appeared with a loud bang in the building before it collapsed, although there has been no official explanation for the accident.

Building collapses are not uncommon in Kenya, as contractors cut corners to keep up with a construction boom in and around the capital.

A six-storey building crumbled in downtown Nairobi in 2006, claiming the lives of 14 people and injuring over 100.(dpa)