German authorities are on the hunt for an a man who added poison to food, including baby food in an attempt to blackmail supermarkets.

Police said a "very unscrupulous" person had added potentially fatal amounts of poison to five bottles of baby food in grocery stores in the southern town of Friedrichshafen. He threatened to continue poisoning food in other stores if his demand for a multi-million euro payment is not made, police said, according to The Local.

In an email reportedly sent on Saturday (23 September) to police and several large supermarket chains, including Aldi, Lidl, Edeka and Rewe, the suspect demanded a ransom of at least €10m (£8.8m).

The email claimed that the blackmailer planned to poison food in supermarkets and pharmacies across Germany and abroad if his demand was not met.

The letter also named certain shops in Friedrichshafen, near Lake Constance, the Local reported. Authorities discovered products with dangerous substances, prompting them to remove all baby food from the shelves before they were sold.

Authorities noted that poisoned food has only been found in grocery stores in Friedrichshafen. Regardless, police have launched a cross-border manhunt.

"This is an exceptionally severe case of extortion and we have to assume we [are] dealing with a very ruthless extortionist who is prepared to kill," said local police chief Uwe Stürmer.

According to the Local, police have asked the public to be on the look out for signs of food tampering and have released a surveillance image of the suspect. The man pictured appears to be around 50 years old, wears glasses and a white hat.

The substance detected was ethylene glycol, which is used in anti-freeze products and brake fluids, a state consumer protection ministry official said. Ethylene glycol is a sweet-tasting chemical that can be lethal to adults and babies, The Telegraph reported.