Kenyan officials have appealed for help to find containers of a highly toxic chemical that were looted from an overturned lorry near the capital city, Nairobi.

Sodium cyanide is dangerous and can kill if swallowed or inhaled even in small amounts, health officials warned, adding that it also poses a major risk to the environment.

It is not uncommon in Kenya for trucks to be looted following a road accident - after the lorry overturned late on Saturday several containers were taken by people who rushed to the scene.

The government urged people to avoid the site, which is on the busy Nairobi-Nakuru highway, while the US embassy advised its citizens to take a detour.

The accident happened about 35km (22 miles) from Nairobi, and caused a spillage on the tarmac.

It is unclear what caused the lorry to overturn. The authorities have also not released details about the condition of the driver.

The national environmental agency urged the public to immediately alert the nearest police station if they spot the containers.

“The public is also cautioned against coming into contact with the contents of containers, which are white substances in pellets form,” agency said.

Kenya's health ministry said the chemical should only be handled by people wearing protective gear.

“Sodium cyanide interferes with oxygen use, leading to rapid death if ingested or inhaled in high doses. Symptoms include headache, dizziness, rapid breathing, nausea, vomiting, and convulsions,” it said.

Sodium cyanide can contaminate soil and groundwater, the ministry said, adding that the chemical can last in the environment for a long time and consequently accumulate in the food chain.

Commercial uses of sodium cyanide include fumigation, extracting gold and silver from ores and chemical manufacturing, according to the US National Institute for Occupational Safety and Health.

Local media reported that while some people carted away containers of the chemical, others who came with jerry cans left without taking anything after realising that the substance was of no use to them.