Two schoolgirls have confessed to stabbing to death a 12-year-old girl in Germany, police said Tuesday, in a case that has shocked the country.

The victim, known only as Luise, went missing on Saturday afternoon after leaving a friend's house near the town of Freudenberg, in the western state of North Rhine-Westphalia.

Luise's body was found the following day in a wooded area not far from her home.

"The child died as a result of numerous knife wounds and the resulting loss of blood," Koblenz prosecutor Mario Mannweiler told a press conference, adding that there was "no indication of a sexual offence".

Two girls, aged 12 and 13, had confessed to the murder, added Florian Locker, head of Koblenz police's homicide department.

The two girls "made statements about the matter and in the end admitted the crime", Locker said.

The girls and Luise knew each other, Mannweiler added.

But he declined to give further details because of the age of the suspects, who are too young to be held criminally responsible for their actions in Germany.

In Germany, the age of criminal responsibility starts at 14 years.

Investigators had yet to find the knife or knives used in the attack, Mannweiler added.

"This is of course a very unusual and shocking act, even for us," Mannweiler told reporters.

Luise had been meant to walk home from her friend's place but her parents raised the alarm on Saturday evening after she failed to return.

Her disappearance sparked a massive search operation that included dozens of police, a helicopter, drones and sniffer dogs.