|Search ON THIS DAY by date|
The tragedy happened at Lake Nyos, about 200 miles (322 km) northwest of the capital, Yaoundé, during the night.
Most of the victims died in their sleep.
The gas killed all living things within a 15-mile (25km) radius of the lake, and the area is still highly contaminated.
It is not yet known what caused the gas to escape the lake, which lies in a volcanic crater.
Government officials say the most likely cause is a volcanic eruption in Lake Nyos which created a fissure, leaking gas into the atmosphere.
But independent scientists say this is unlikely, as the volcano is believed to be extinct.
Cameroon radio is reporting that gases are continuing to escape from the lake.
Rescue teams wearing gas masks have been rushing cylinders of oxygen to the remote area to help any who may have survived.
Hundreds of people have been arriving in the main hospital in Yaoundé for treatment.
A doctor there said they had been poisoned by a mixture of gases including hydrogen and sulphur.
He described the symptoms, including burning pains in the eyes and nose, coughing and signs of asphyxiation similar to strangulation, as like being gassed by a kitchen stove.
Eyewitnesses described how the normally clear waters of the lake turned a reddish brown, while a sudden wind arose and whipped up huge waves.
The gas is believed to have overwhelmed at least three villages.
The entire population of one of the villages is thought to have been killed.
There was a similar escape of toxic gases at a nearby lake in the same volcanic crater two years ago which killed 37 people.
The cause of that disaster, too, remains a mystery.
Scientists from the United States and France are on their way to investigate the lake.
They will bring with them rescue teams and emergency aid to help the survivors.
The US has pledged $25,000 in immediate aid, while France, Britain and other Western European countries have promised logistical support.
The Israeli Prime Minister, Shimon Peres, has said he will not cancel his state visit to Cameroon, due to start on Monday.
He said he would be bringing a medical team and equipment for treating the victims.
The eventual number of people who died in the Lake Nyos gas leak was put at more than 1,700.
Scientists debated the cause of the disaster for some time afterwards.
It was finally concluded that the lake's lower levels had become saturated by carbon dioxide gas (CO2) due to gaseous springs which bubbled up from the extinct volcano beneath.
It is thought that recent high rainfall had displaced the CO2-rich water at the bottom, releasing a massive bubble of carbon dioxide gas from the lake in a natural phenomenon now referred to as "lake overturn".
The heavy gas then sank to the ground and rolled in a cloud several tens of metres deep across the surrounding countryside.
Pipes have now been put in place in Lake Nyos and nearby Lake Monoun to siphon water from the lower layers up to the surface and allow the CO2 at the bottom of the lake to slowly bubble out, preventing a repeat of 1986 tragedy.
Following the Nyos tragedy, a survey was carried out into the CO2 content of other African lakes.
It revealed that Lake Kivu, in Rwanda, is becoming saturated with carbon dioxide just as Lake Nyos was, and is seriously at risk of lake overturn.
Scientists have warned that if nothing is done, millions of people living around Lake Kivu are in danger.
|Search ON THIS DAY by date|