A grove containing some of the world’s oldest giant sequoia trees is under threat from a rapidly growing wildfire at California’s Yosemite national park.

From Friday to Sunday, the blaze expanded from 250 acres to roughly 1,600 acres, with the terrain of timber and brush fueling the flames, officials said. Visitors on the Washburn Trail of the Mariposa Grove of Giant Sequoias first reported the blaze on 7 July, and more than 400 firefighters have gone out to try to contain it.

The firefighters’ efforts included laying down a sprinkler system within the grove to keep the trunks of more than 500 mature giant sequoias moist. Officials also hope the steady spray of sprinkler water keeps the flames away from the grove, which they had also previously protected with so-called prescribed burns aimed at clearing out materials that could help fuel fires.

None of the grove’s named trees – including the 3,000-year-old Grizzly Giant – had suffered significant damage as of Sunday. But the area where firefighters are working is difficult and prone to keep fires burning, especially because a high number of trees that died in a three-year period beginning in 2013, officials said.