Nairobi - At least four people were missing after the collapse of a seven-storey building in the Kenyan capital Nairobi overnight, the Red Cross said on Tuesday. The incident occurred in a very poor neighbourhood near Nairobi's international airport southeast of the capital, Red Cross spokesperson Noellah Musundi told AFP.She said the exact number of people missing was unclear, but confirmed rescuers were looking for a mother and her three children. Police and local residents said the authorities were alerted on Monday after cracks appeared in the building, prompting an urgent evacuation before it collapsed two hours later, at around 1900 GMT. "The collapse was not completely unexpected, which allowed us to evacuate most of the people," said Musundi of the incident which occurred in the Kware area of Mukuru Kwa Reuben, one of the biggest slums in Nairobi. Resident Dorothy Ouko told AFP she was worried about her 15-year-old son and 22-year-old nephew who had insisted on finishing their dinner before leaving the building. "My three other kids were out of the house when it collapsed," she said, adding that one of her neighbours on the sixth floor had also insisted on staying, dismissing fears the building would collapse. "She was in the house with her two children and we don't know where they are now or whether they are alive." Trapped under the rubble? By midday, 128 tenants had been accounted for, the National Disaster Management Unit said. It was not immediately clear how many people were living there."Most families cooperated and (were) evacuated safely. However, it is believed that some people may have been trapped. Rescue efforts are ongoing," said spokesperson Pius Masai.The ruins of seven-storey building is pictured after it collapsed overnight in the Nairobi suburb of Embakasi. (AFP) He said the rescue operation was difficult since space was limited and the adjacent seven-storey building also appeared to be unstable."It is a very delicate operation but we hope to finish it safely," he said.Tenants from the neighbouring building were also evacuated, he said.No planning permission Images posted on Twitter by the Kenyan Red Cross showed work to clear the rubble with the help of an excavator, with parts of the building's red roof clearly visible.Rescue personel work at the scene after a seven-storey building collapsed overnight in the Nairobi suburb of Embakasi.(AFP) A fire engine was also on site as well as a number of soldiers.Masai, National Disaster Management Unit spokesperson, also appealed for anyone with cutters or drilling equipment to join the search and rescue operation. Quoting City Hall, The Star newspaper said the structure was built in 2007 without planning permission or approval. "Kware area was unplanned. No developments are allowed there. But you find that most of these developers were brought by politicians," Nairobi Lands executive Christopher Khaemba told the paper.Police are reportedly looking for the owner of the building.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 little regard for regulations.People gather at the scene as rescue personel works after a seven-storey building collapsed overnight in the Nairobi suburb of Embakasi. (AFP)Such incidents have raised questions about the quality of building materials and construction standards in a country where rampant corruption has seen unscrupulous developers using bribes to avoid regulations.In April 2016, 49 people died when a six-storey building collapsed in a poor neighbourhood northeast of the capital following days of heavy rain which caused floods and landslides.The building, constructed two years earlier, had been slated for demolition after being declared structurally unsound. Although around 150 families were living there in tightly-packed conditions, an order to evacuate the building and demolish it was ignored.