The incident has been reported to police, the university added.

The samples were stored in tanks cooled with liquid nitrogen, at a temperature of minus 190 degrees Celsius (minus 310 degrees Fahrenheit), at the medical university Karolinska Institutet (KI) in Stockholm.

KI is home to the Nobel Assembly, which is tasked with selecting a winner for the Nobel Prize in Physiology or Medicine.

Sometime between December 22 and 23 there was an interruption in the supply of liquid nitrogen to 16 cryogenic tanks, and while the tanks can go for four days without additional liquid nitrogen, they were left without it for five, leading to the destruction of samples from multiple institutions.

“It happened at possibly the absolute worst time imaginable in Sweden, just one day before Christmas Eve,” Matti Sällberg, Dean of KI’s southern campus, told AFP.

Some media outlets reported that the estimated value of the samples lost was some 500 million kronor ($47 million). Sällberg said no official estimate of the value of the samples lost had been made, but said it was easily in the millions.

“Those worst affected are those researching leukaemia, they have gathered samples from patients over as much as 30 years,” Sällberg said.

An internal investigation has been launched at the university and despite there being no indication of sabotage, the incident has also been reported to police.

“Currently there is no indication that it was due to outside influence, but the police report was done to cover all bases,” Sällberg said.

The samples were all strictly for research so it would not affect the care of any current patients, but had been intended to be used in future research.

“These are samples that have been the subject of extensive studies and there were plans for more studies,” said Sällberg.