His school, the Monterrey Institute of Technology, said in a Twitter post that he was in stable condition and expected to recover, though it did not release his name.
The man was in a van with other students two Germans, two French and six Mexicans traveling back from Acapulco and passing through the Guerrero state capital of Chilpancingo just after a confrontation between police and kidnappers that killed one officer.
Police tried to stop the van, believing it was suspicious. Police said they opened fire when they heard something that sounded like shot or detonation, said Victor Leon Maldonado of the Guerrero state prosecutor's office.
The German student was shot in the buttocks. Maldonado told reporters in a press conference that the officers shot at the bottom of the van, trying to hit the tires to make it stop.
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The police involved have been detained and their weapons are being tested, according to a statement from the state attorney general's office.
The shooting came two weeks after police in another Guerrero city, Iguala, opened fire on teacher's college students, killing six and leaving 43 other missing.
The September 26 confrontation in Iguala shed light on a widespread problem with local police in Mexico: They are often linked to organized crime.
In the case of Iguala, the police who attacked the students were working with the local cartel, Guerreros Unidos, according to testimony of those arrested.
A US State Department travel warning issued last week said US citizens should avoid Chilpancingo along with all parts of the state outside of the Pacific resorts of Acapulco, Ixtapa and Zihuatanejo and the tourist attractions of Taxco and the Cacahuamilpa caves.