California firefighter dies battling wildfire sparked by gender reveal party

The firefighter's name is being withheld pending next of kin notifications.

A California firefighter died Thursday while battling a massive wildfire sparked during a gender reveal celebration over the summer, officials said Friday.

Authorities have not released the firefighter’s identity, but they said he died in the El Dorado Fire, a 21,000-acre wildfire in the San Bernardino National Forest in Southern California, according to the U.S. Forest Service. His name is being withheld pending next of kin notifications.

"Our deepest sympathies are with the family, friends and fellow firefighters during this time," the Forest Service said in a statement, noting that the cause of the death was under investigation.

The El Dorado Fire, which erupted Sept. 5 near Yucaipa, was about 66% contained on Friday morning as crews battled to keep it from spreading toward a busy highway.

Officials said the blaze was caused by a smoke-generating pyrotechnic device used during a gender reveal party.

Dozens have died since a string of wildfires broke across the West, scorching more than 5 million acres of land in California, Washington and Oregon, and forcing hundreds of thousands of people to evacuate their homes.

As of Friday, there were at least 50 active wildfires blazing in Oregon and California, sending heavy smoke as far east as Europe, according to satellite images released by the European Union's Copernicus Atmosphere Monitoring Service.

ABC News' Bonnie Mclean contributed to this report.