Germany's biggest outbreak of food poisoning, in which more than 11,000 schoolchildren have been laid low by diarrhoea and vomiting, is "very likely" to have been caused by a batch of frozen strawberries, authorities said on Friday.

Children in almost 500 schools and daycare centres across eastern Germany that received food from a subcontractor of the catering firm Sodexo have been affected, and at least 32 have been treated in hospital.

The Robert Koch Institute, which advises the German Health Ministry on infectious diseases, said it had found a "strong and statistically significant link" between the outbreak and "consumption of products made from a batch of frozen strawberries".

Many of the patients were found to be infected with noroviruses, it said in a joint statement with a task force set up by the government and affected states.

Sodexo announced that it planned to compensate victims and said further details would be announced in the next few days.

In a statement, it apologised to the children and their families for "an extremely regrettable one-off incident" and said it would select its suppliers "even more rigorously" in future.