This capital and six of Mexico's 31 states were on alert Wednesday after the theft of what U.N. nuclear regulators described as "extremely dangerous" radioactive material used in medicine.
A truck carrying a teletherapy source containing cobalt-60 was stolen Monday in Tepojaco, a town in the central state of Hidalgo.
The vehicle was en route from a hospital in the northern border city of Tijuana to a storage facility for radioactive waste.
The search for the truck and its potentially dangerous cargo is focused on Mexico City, Hidalgo, the central states of Mexico, Queretaro, Tlaxcala and Puebla and the Gulf coast state of Veracruz.
The source containing the cobalt-60 is "shielded and does not represent a risk" as long as the vessel is not broken or tampered with, Hidalgo undersecretary for emergency services Miguel Garcia Conde told Efe.
Should the shielding be breached, anyone in close proximity to the radioactive material would be in grave danger, he said, though adding that "we are not talking about a community exposed to radiation."
Mexican authorities have issued an appeal to the thieves to leave the container intact.
"There is a high probability (the truck) is no longer in the state of Hidalgo," Garcia Conde said.
The International Atomic Energy Agency said Wednesday that it learned of the theft from Mexico's National Commission for Nuclear Safety and Safeguards.
"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," the IAEA said in a statement. EFE