SHANGHAI — Regulators are investigating whether restaurants throughout China are creating food hazards by cooking with recycled oil, some tainted with food waste, and prominence given to the issue in the state-controlled media suggests that the problem could be widespread.

The State Food and Drug Administration issued a nationwide emergency notice telling health bureaus to investigate the sources of cooking oil in mid-March. The notice came shortly after a professor and a group of students at Wuhan Polytechnic University announced that they had found widespread use of recycled oil in their region in an undercover investigation. The professor, He Dongping, asserted that recycled oil was being used to prepare 1 in 10 meals in China.

Regulators are now searching for illegal oil recycling mills, and some health bureaus have begun releasing the names of restaurants and food establishments that were found to be using questionable oil.

Last November, regulators in southern China raided several workshops for turning discarded waste — possibly even sewage — into cooking oil.