People on boat aver Danube river taking picture during summer night ride [Stock image of Danube river used for illustrative purposes only] Image Credit: Supplied

LYON - International police organisation Interpol appealed for help from the public on Tuesday in the case of a dead boy found in the Danube river that has mystified German police.

The boy, estimated to be five or six years old, was found in May last year in Bavaria, weighed down with a flagstone slab and wrapped in foil, Interpol said in a statement.

German police, unable to identify the body or the circumstances of his death, asked Interpol to issue a "Black Notice", an international alert to gather information on unidentified bodies.

Interpol said it was not known how long the body had been in the water when it was found on May 19, 2022, near Grossmehring, a Bavarian municipality of 7,500 inhabitants.

He was approximately 110 cm (3 foot 7) tall, weighed 15 kilograms (33 pounds), and had brown hair and blood type 0.

Police think the boy spent time outside Germany, which is why Interpol's 195 member countries may be able to shed light on his death and "whether he was victim of trafficking, abduction or violence", said Juergen Stock, the organisation's secretary general said.

"Someone, somewhere knows something about this boy," he said in the statement.

Members of the public, "particularly those who remember a missing child whose characteristics and disappearance indicate a potential link to the case", are invited to contact the German police, Interpol said.

It said the "I-Familia" tool, which it started operating in 2021 to identify unknown bodies through international family DNA kinship matching, could become useful in the case.

The investigation falls under the "Identify Me" programme framework, launched earlier this year and aimed at cold cases.

Identify Me, created to help identify 22 suspected female murder victims, has received more than 500 messages and tips from the public, Interpol said.