Health officials are looking for Kenyans who attempted to steal from a truck that overturned near Limuru.
Videos taken at the scene showed some Kenyans turned up with 20-litre jerrycans before realising the truck was not carrying oil or liquid that they recognised.
Instead, the truck was carrying sodium cyanide, an extremely dangerous poison commonly used to refine gold.
The Ministry of Health said half a gramme can kill a grown man in two to six hours if ingested.
Health officials in Kiambu said anyone suspecting they were exposed should turn up in hospital immediately.
“Death can take longer depending on the dose ingested or how the body reacts,” said a public health official who visited the area.
The Ministry of Health on Sunday cancelled a press conference scheduled at the scene in Kambembe, Rironi, in Kiambu county, over safety concerns.
Health PS Mary Muthoni had earlier warned the public to avoid the scene of the accident.
The truck overturned on Saturday.
“The ministry advises the public to avoid the site of the incident and to cooperate with our emergency and disaster response teams as they work to contain the situation,” she said.
The chemical was last week blamed for the highly publicised deaths of six people in a luxury hotel in Bangokok, Thailand.
Sodium cyanide mostly comes in the form of white powder but it is sometimes transported in liquid form.
The heart, respiratory system and central nervous system are most susceptible to cyanide poisoning.
It is used in a number of industries, such as metal refinery.
In Kenya it is popularly used as the main ingredient in gold leaching.
Kenya has strict regulations on handling and transport of the chemical. For instance, it must be transported in an openly marked vehicle showing its contents.
However, most of the chemical used in Migori gold refineries is smuggled in from Tanzania.
According to the Global Initiative Against Organised Transnational Crime, a tonne of cyanide is between Sh400,000 and Sh500,000.
However, legal cyanide in Kenya goes for between Sh600,000 and Sh700,000, the initiative says on its website.
On Saturday, PS Muthoni noted ingestion or inhalation can cause immediate symptoms such as headache, dizziness, shortness of breath, nausea and vomiting.
"Severe exposure can lead to loss of consciousness and convulsions within minutes."
Prolonged or repeated exposure to lower levels can result in long-term health issues including neurological damage, thyroid dysfunction and cardiovascular problems, she said.
In terms of environmental hazards, the PS noted that Sodium cyanide can pose a significant threat to aquatic life.
She said any accidental release into waterways can cause extensive fish kills and long-term damage to aquatic ecosystems.
"Although sodium cyanide can degrade over time, its initial impact is often devastating," she said.
Muthoni has also recommended proper personal protective equipment when handling it to prevent direct exposure.
She, however, noted that the ministry remains committed to ensuring public safety and managing the risks associated with it.
"Further updates will be provided as more information becomes available," the statement reads.