A hunk of rock “the size of an apartment building” has fallen off the famous granite face of El Capitan in Yosemite national park in California, killing one person and injuring another.

At least 30 climbers were on the wall at the time of the accident on Wednesday afternoon, but it was not clear if the victims were climbers or tourists, ranger Scott Gediman said.

“It’s the heart of climbing season,” Gediman said. “It was witnessed by a lot of people.”

UPDATE: A viewer sent us a photo of the rock fall at El Capitan in #Yosemite that killed 1 person and injured more. https://t.co/pXouFj7ivH pic.twitter.com/bSJoRP9rQo — KSEE24 News (@KSEE24) September 28, 2017

The injured person was taken to a hospital near the park. No names were immediately released.

El Capitan is one of the world’s largest granite monoliths towering 4,000ft (1,219m) above Yosemite Valley.

Several people made emergency calls, reporting that the rock fall occurred on the Waterfall route on the east buttress of El Capitan.

Officials did not provide details on the size of the rock fall, but climbers posted pictures on social media from hundreds of feet up the wall showing billowing white dust moments after the crash.

“I saw a piece of rock, white granite the size of an apartment building, at least 100 feet by 100 feet, suddenly just come peeling off the wall with no warning,” said Canadian climber Peter Zabrok, 57, who was scaling El Capitan and was above the rock fall.

Zabrok said he has climbed El Capitan dozens of times and has “never seen anything like this”.

Mountaineers travel from around the world to scale the sheer face and this time of year is the peak season for attempting the climb because the days are long and not too hot.

Ken Yager, president and founder of the Yosemite Climbing Association, reviewed photos of the cliff face and debris field, estimating the relatively thin piece that broke off covered an area big enough to fit five houses.

“It cratered and sent stuff mushrooming out in all directions,” said Yager.

Rock falls are common in Yosemite but seldom fatal. Kevin Jorgeson said he and climbing partner Tommy Caldwell witnessed a massive rock fall in the same area while they prepared for a trek that made them the first people to free-climb the Dawn Wall route on El Capitan in 2015.

“Yosemite is just a really active, wild place. It’s always changing,” Jorgeson said. “It doesn’t make it any less tragic when someone gets in the way of that.”

