Tragedy has struck a prominent German family.

Steakhouse heiress Christina Block's children Klara, 13, and Theodor, 10 were kidnapped while watching fireworks with their father Stephan Hensel at a New Year's Eve celebration close to the Germany-Denmark border, according to German newspaper Bild, per a translation by People.

The alleged abduction took place at a restaurant in the Danish town of Gråsten shortly after midnight on Jan. 1, when a group of men knocked Hensel to the ground and forced the kids into two cars, local police said, per U.K. outlet The Telegraph. The vehicles—a Mercedes-Benz and a Citroën—bared German license plates, according to the publication, though it is unclear if they crossed the border after the incident. 

Klara was last seen wearing light cargo pants and a green sweater with a teddy bear on the front, per The Telegraph. Meanwhile, her brother Theodor was in light blue jeans, a blue-and-white striped shirt and a dark pullover.

Both Danish authorities and German police have launched an investigation into the matter.

The kidnapping comes amid a custody battle for the children between Block and Hensel, who divorced in 2018, according to The Telegraph.

Per the outlet, a police official said investigators are looking into "whether there is a connection between the night's events and the question of parental authority."

Block, 49, is the daughter of restauranteur Eugen Block, who founded the Hamburg-based steakhouse chain Block House in 1968. Her father's fortune is estimated to be worth $330 million, according to the German newspaper Hamburger Abendblatt.

Neither she or Hensel have publicly spoken out about the incident.

E! News has reached out to German and Danish authorities for comment but has not heard back.