An unidentified Scrooge poisoned visitors to two of Berlin's popular Christmas markets with an offer of tiny bottles of liquor that were laced with vomit-inducing chemicals, police said Friday.

The suspect, who was in his mid-40s, hit two of the traditional holiday fairs Thursday and at the first, spoke to two foreign students, a man and a woman in their mid-20s, in English.

"He told them about the purported birth of his daughter and handed out little schnapps bottles for a toast," police said in a statement.

"After they drank, the two victims began experiencing severe cramps and vomiting."

The woman lost consciousness and had to be hospitalised.

Later at another Christmas market, what appeared to be the same blond man approached a group of three women in their early 20s with the same story. They also accepted a drink and later had to be treated in hospital.

"In this context, the police advise special vigilance," authorities said.