Mexican authorities scrambled Wednesday to find a stolen truck containing "extremely dangerous" radioactive material used in medical treatment, officials said.

The white Volkswagen Worker truck was transporting a "teletherapy source" containing cobalt-60 when it was stolen in the central Hidalgo state town of Tepojaco, north of Mexico City, the International Atomic Energy Agency said.

The IAEA said the material came from a hospital in the northern city of Tijuana and had been on its way to a radioactive waste storage center. It said the truck was stolen at a service station.

"At the time the truck was stolen, the source was properly shielded. However, the source could be extremely dangerous to a person if removed from the shielding, or if it was damaged," an IAEA statement said.

The IAEA said it was informed about the theft by Mexico's National Commission for Nuclear Safety and Safeguards (CNSNS).

The CNSNS said the radioactive material was inside a "properly shielded" medical container and posed no risk provided it was not broken or tampered with. It said the truck was stolen at a service station.

A search was underway in six states and in Mexico City for the white Volkswagen Worker truck, which has an integrated crane, the CNSNS said in a statement.

It gave phone numbers for anyone with information to call and released photos of the steel-reinforced wooden crate carrying the material.

Mexico's drug cartels have branched out to other illegal activities, stealing oil by piercing pipelines and extracting coal and iron ore, but officials have not said who the thieves might be.

Experts have long warned about the risks posed by the large amounts of radioactive material held in hospitals, university campuses and factories, often with little or no security measures to prevent them being stolen.

Such material is highly dangerous to human health if not properly handled.

Theoretically could be used in a 'dirty bomb'

Cobalt-60 "has figured in several serious source accidents including fatalities because the material was obtained and handled by people who were not aware of its danger," said Mark Hibbs, analyst at the Carnegie Endowment for International Peace.

"There are many thousands of these sources worldwide. There is in most countries a regime to keep them safe and secure, but if they are stolen or lost, many people would be unaware that the radioactive contents locked up inside could threaten their lives," Hibbs told AFP.

More worryingly, though, such material could in theory be put in a so-called "dirty bomb" -- an explosive device designed to spread the radioactive material over a wide area.

Major international efforts have been made since the end of the Cold War in 1991 and the September 11, 2001 attacks in the United States to prevent nuclear material falling into the wrong hands.

US President Barack Obama hosted a summit in 2010 on the subject, followed by another in Seoul last year. A third is planned in The Hague in March 2014.

IAEA chief Yukiya Amano said in July at a major nuclear security conference that many countries had taken effective measures but warned against a "false sense of security".

"If a 'dirty bomb' is detonated in a major city, or sabotage occurs at a nuclear facility, the consequences could be devastating," Amano said.

A report issued in July by the Arms Control Association and the Partnership for Global Security said progress had been made reducing the threat but that "significant" work remained.

In an incident showing how dangerous such materials are, in Goiania, Brazil in 1987 a machine containing a substance similar to cobalt-60, caesium-137, was left lying around after a cancer unit of a hospital moved.

Thinking it might have scrap value, two people dismantled the equipment and when the radioactive material started glowing blue in the dark it was shown off around the local community as a curiosity.

Eighty-five houses were contaminated and 249 people needed medical treatment. Twenty-eight people suffered radiation burns and four died including a six-year-girl who handled the substance while eating.