Denver, Jun 22 (IANS): Several attendees of a concert at the Red Rocks Amphitheatre in Colorado where former One Direction member Louis Tomlinson was scheduled to perform, were injured after they were hit by "apple-sized" hail, officials said.

In a statement on Wednesday night, West Metro Fire Rescue, which responded to the emergency, said the number of potential patients and the extent of their injuries were not immediately known, the Colorado-based The Gazette newspaper reported.

A concert goer called it the "scariest night of (her) life".

"It started pelting people with hail at Red Rocks and my sister and I luckily found shelter under a sign. I am bleeding and have huge bumps on my head from the hail. Hoping everyone made it out safely," the newspaper quoted her as saying.

Another person said the hail that fell down "was literally apple sized", adding the that "ground looked like it snowed. My partner's windshield is literally shattered".

The concert has been delayed and Red Rocks Park and Amphitheatre advised concert goers to "seek shelter in your vehicle", adding, "we'll let you know when we've received the all clear".

The Red Rocks Amphitheatre is an open-air amphitheatre built into a rock structure near Morrison, Colorado.

There is a large, tilted, disc-shaped rock behind the stage, a huge vertical rock angled outwards from stage right, several large outcrops angled outwards from stage left and a seating area for up to 9,525.