The discovery of a seventh planet around a distant star makes it one the richest planetary systems yet discovered, European astronomers say.

The discovery at the dwarf star KIC 11442793, reported by two separate teams of researchers, could be a record, they said.

One of the identifications was credited to volunteers using the Planet Hunters website set up to allow citizen scientists to sift through the public data from NASA's Kepler space telescope, which has been searching for exoplanet candidates orbiting distant stars.

The system bears some similarities to our own, although all seven planets orbit much closer to their host star some 2,500 light years from Earth, a researcher for the second team at Britain's Oxford University said.

"It actually looks like our Solar System in one sense, with all the small planets on the inside and the big planets on the outside," Robert Simpson told the BBC. "And that's not necessarily what we always see."

However, all seven planets' orbits would fit within the Earth's distance from the Sun, making for a crowded solar system, astronomers said.