The head Mexico's national emergency services, Luis Felipe Puente, warned on Monday that an unknown amount of nuclear material used in medical equipment had been stolen from the back of a truck in Tlaquepaque, Jalisco state.

"This was industrial equipment that included Iridium-192... which can be dangerous for people if it is taken out of its container," the interior ministry said in a statement.

The theft prompted an alert and search for material across nine states: Jalisco, Colima, Nayarit, Aguascalientes, Guanajuato, Michoacan San Luis Potosi, Durango and Zacatecas.

Puente urged anyone who uncovers the substance to report it and stressed not to open it. Anyone who finds it should be sure to stay back 30 meters (yards) and immediately contact authorities for help, he said.

Since 2013, there have been at least seven cases across Mexico of radioactive materials being stolen or being lost. Last year, a container of radioactive material used In X-rays was stolen along with a car. In all cases the material was returned without incident.

dm/bw (AP, Reuters)