Residents of Nairobi South have raised concerns over toxic emissions being discharged by some factories operating in the area.
They say that since the emissions started two weeks ago, cases of respiratory ailments have increased.
Many children have been coughing, vomiting and nose bleeding.
The residents - living in estates along Mombasa Road - complain that some factories have been discharging the poisonous gases at night.
Ms Jane Ndambuki, a resident, said that the smell, which is similar to that of burning tyres or teargas, irritates the nose when inhaled.
"We just want to know what it (the gas) is, and which factory is emitting it. On Saturday, the emissions started from 4pm and intensified in the night, we woke up choking," the mother of two said on Monday. She said that the same was experienced a few years back.
Ms Njeri Wang'ombe said that her one-year-old baby coughed and vomited after inhaling the strange gas at 3am.
"At first I thought she had developed asthma, but when I later inhaled the gas and started coughing," she said.
Ms Elizabeth Yego recounted how she developed breathing difficulties after inhaling the poisonous gas at night.
"The pungent smell was too much to handle and it has been going on for a while now. We are worried about our children," Ms Yego told Nation.co.ke on Monday.
Nairobi County Assembly Majority Whip and South B Ward Representative Waithera Chege said that she experienced the pungent smell first on Saturday while driving along Mombasa Road. She now wants National Environment Management Authority (Nema) to investigate the source of the poisonous gas.
"We will not allow companies to make money at the expense of citizens' health. This is a public health issue that can lead to respiratory complications," said Ms Chege.
The MCA gave Nema 14 days to find a lasting solution to the problem by preparing a full report showing the location of the companies and a full disclosure of the owners, failure to which she will petition for the disbandment of the agency.
"It is within their (Nema's) mandate to deal with this issue but they have done nothing. I want them move with speed to save many lives that are now at stake. I will also bring the issue before the Assembly on Tuesday," she said.