Hungarian rescue officials said there was little chance of finding survivors after a boat with South Korean tourists on board sank on the Danube River in Budapest, with seven people confirmed dead and 21 missing.

The boat was cruising when it collided with a larger luxury passenger boat during a rainstorm on Wednesday evening, causing it to capsize and sink with 33 South Korean tourists and tour guides and two Hungarian crew aboard.

"I wouldn't say there is no hope, rather that there is a minimal chance (of finding survivors)," Pal Gyorfi, a spokesman for the Hungarian national ambulance service, told the M1 state broadcaster.