Russian authorities on Wednesday announced plans to clean up more than 160 tonnes of highly toxic waste that was illegally dumped close to a town after outraged residents appealed to the Kremlin.

A chemical company dumped 163 tonnes of carbon tetrachloride in an abandoned asphalt plant near the small town of Balezino in the Udmurtia region of central Russia.

The town's residents late last week wrote a letter to President Dmitry Medvedev asking him to intervene and accused the regional government of putting 40,000 people at risk.

"The (regional) administration had known about the crime since the end of December but had thoroughly covered it up until March 14, 2012, when the information was revealed on national television," said the letter posted online.

"No practical measures had been taken over that period to eliminate the danger," it said, adding that investigators only began looking into the illegal dumping on March 14.

"The lives and health of nearly 40,000 residents of the district are in extreme danger."

When heated to high temperatures, carbon tetrachloride can generate poisonous phosgene gas, which was used as a weapon during World War I.

"It is known that the substance is extremely poisonous and inhaling even a small dose causes death within 14 weeks," residents of Balezino said in the letter.

"The substance begins to intensively evaporate at a temperature of 15 degrees (Centigrade) below zero," they said.

The arrival of spring would increase the evaporation of the chemicals which are likely to find their way into ground water as the snow begins to melt, they added.

The regional government of Udmurtia claims the deadly substance was stored in a pit under a 30-centimetre (one-foot) layer of ice and therefore does not pose an immediate health risk.

The chief of staff of the deputy head of the regional government, Robert Bogdanov, said work to remove the waste from the pit would begin Friday.

"We've adopted a plan. We are planning to begin the work on Friday," he told AFP after the authorities held an emergency meeting earlier on Wednesday.

The chemicals will be loaded into plastic containers and moved to a specially designated waste dump, Bogdanov added.

Russian natural resources minister Yury Trutnev earlier this week set up a special task force to coordinate the work of various government agencies in assessing the environmental damage.

The Federal Service for Hydrometeorology and Environmental Monitoring examined the air near the pit on March 16 and concluded that it was highly polluted, the natural resources ministry said.

"The results of the inspection showed that within 10 metres of the burial site a characteristic odour could be smelled in the air," it said in a statement.

"This is a sign of extremely high levels of air pollution."

Authorities said Monday that prosecutors had summoned representatives of the chemical company that dumped the waste, Khimprom, based in the nearby region of Chuvashia, to their offices.

Asked if Medvedev received the letter from Balezino, a Kremlin spokeswoman said she was unaware of the situation.

"Thousands of people and residents write to the president," she told AFP.

Last summer the Kremlin chief said he was alarmed over the amount of toxic waste stored in Russia, estimating that it amounted to more than 30 billion tonnes.