At least 51 people were injured by lightning strikes at the "Rock am Ring" music festival in western Germany on Friday evening, according to German police, with forecasts of thunderstorms and possibly hail to come.

Organizers could not be reached for comment about any plans to shut down the festival, which is now in its 31st year and takes place at the airport in Mendig, a small town located about 150 km from Frankfurt, near the Nuerburgring motor racing track.

The festival organiser had reported on its website early Saturday morning that at least 42 people were injured, eight seriously.

But the numbers rose as more fans reported injuries in the early morning hours, according to the police spokesman.

Thirty-three people were injured at the festival by lightning strikes last year, according to German media.

Deutsche Welle said this year's festival was attended by around 45,000 people.