A woman was killed and at least three other people were injured by a lightning strike Friday in Rocky Mountain National Park, the National Park Service and local authorities said. The three injured people were listed as stable at Estes Park Medical Center, where four more people were also treated and released, after the lightning bolt hit about 1:20 p.m. (3:20 p.m. ET) on the Ute Crossing Trail.

"We can't emphasize enough that when it starts to get dark and the clouds are forming, it's time to get down," Martin Koschnitz, the hospital's medical director, told NBC station KUSA of Denver. "My understanding is this group was actually in the process of doing that and still got caught. This is really a sad thing."

A plume of smoke rises Friday above Longs Peak in Rocky Mountain National Park. Several fires have been burning in the park in recent weeks, some sparked by lightning. Brennan Linsley / AP, file

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Lightning strike kills 1, injures 7 in RMNP http://t.co/h6p9uJcr1A #9NEWS — 9NEWS Denver (@9NEWS) July 11, 2014