German police launched an attempted murder investigation on Tuesday after a poisoning at a university left one student in a critical condition and six others in need of medical attention.

The victims at the Technical University Darmstadt had consumed food or drink, to which a "harmful substance" had been introduced, notably via packets of milk and containers of water, the police said.

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Investigators said packets of milk and water containers were among the items "spiked" over the weekend with a chemical, which they described as having a noticeably "pungent smell."

The affected building was closed off by police and any foodstuffs on site taken away for investigation.

One 30-year-old student was in a critical condition as of Monday, police said. No further victims have been identified.

Authorities recommended anyone displaying potential symptoms or whose "extremities turn blueish" should seek medical help immediately.

"We are shocked by the apparent offense that happened at our university," the university's president, Tanja Bruehl, said in a statement. 

"I wish the affected all the best, a quick recovery and can assure them my full support," Angela Dorn, the science minister for the state of Hesse, which includes Darmstadt, said in a statement.

"Together with the university and investigators, we now need to clarify the situation as quickly as possible," Dorn added.