PARIS (AP) — Three people were killed and a child is missing after a motorized rubber boat capsized Thursday in the Rhine River between Germany and France.

One of those killed was a passer-by who tried to help with the rescue. French and German rescuers are searching for the missing child.

The boat, which left the German bank of the river Thursday morning carrying two adults and two children, sank near the eastern French town of Gerstheim, police said.

Onlookers on the banks tried to help save the sinking group, according to an official with the regional police authority.

Three people were killed — a 6-year-old girl and an adult who had been on the boat, and another adult who tried to save them, the official said. Another adult passenger was hospitalized, and a girl passenger is missing, the official said.

It's unclear what caused the sinking. No information was immediately available about the victims' nationalities.

Helicopters, divers and police and firefighters are involved in the extensive search, according to the regional French rescue service for the Bas-Rhin region.

The crash came after a sightseeing boat packed with South Korean tourists collided with a cruise ship in Hungary's capital, leaving seven dead and 21 missing.