German prosecutors launched an investigation into attempted murder 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, half an hour by train from Frankfurt, had consumed food or drink to which a "harmful substance" had been introduced.
Police say packets of milk and water containers were among the items spiked over the weekend with the chemical, which they described as having a noticeably "pungent smell".
Anyone feeling unwell or whose "extremities turn blue", should seek medical attention immediately, police said, citing one of the potential effects of the poison.
Police said they have called up a team of 40 people to investigate the incident, and are working at "full speed" to identify a culprit.
The affected building, part of the Department of Materials- and Geosciences, was cordoned off and any foodstuffs on site taken away for investigation.
Overnight, forces carried out further searches across the campus but found no "relevant objects".
As of Tuesday, there was "no acute danger", according to authorities.
One 30-year-old student was in a critical condition as of Monday, police said. No update has so far been provided.
- 'Shocked' -
In a statement, the university described the events as a "poison attack".
"We are shocked by the apparent offence that happened," university president Tanja Bruehl said in a statement.
"My sympathy is with those affected, who will receive full medical help," she said.
Public prosecutor Robert Hartmann told the Bild newspaper: "We are taking this very seriously. We can't rule out that we are dealing with an attempted murder here."
Angela Dorn, the higher education minister for the state of Hesse, where Darmstadt is located, offered her "full support" to the victims.
"Together with the university and investigators we now need to clarify the situation as quickly as possible," Dorn said.
Germany has been shocked by several poisoning incidents in recent years.
In December 2019, five newborn babies were poisoned with morphine, but a nurse who was initially arrested for the crime was subsequently released.
The babies, aged between one day and five weeks at the time, all survived the attempted poisoning. No one has been charged over the case.
A German court in 2019 sentenced Klaus O. to life in prison for spiking his colleagues' sandwiches with a poisonous powder containing lead, mercury and cadmium compounds.
He was caught red-handed in 2018 trying to poison other colleagues.