"Condition RED means immediate danger to health so take action to limit further exposure".
The dire warning further stressed the severity of the situation, underlining the gas could affect "the entire exposed population".
It opened over the weekend on the Big Island about 100 feet from Fissure No. 16, which spewed lava for about 250 yards.
The agency said the best way to stay protected from the sulphur dioxide is to leave the areas of inundation.
A driver steers through volcanic gasses in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 13, 2018.
Hawaii's Tourism Authority said the volcanic activity is limited to a remote area on Hawaii's east side.
The executive director of the Island of Hawaii Visitors Bureau told CNN the volcano isn't just the Big Island's No. 1 attraction, "it's the state's No. 1 attraction". No deaths or major injuries have been reported since Kilauea, which has been in a state of almost constant eruption since 1983, began a series of major explosions early this month. Lava flow in the area has paused, but sulfur dioxide gas, which causes acid rain and can be life-threatening, remains a hazard.
The National Weather Service has warned residents of "light ashfall" throughout the day in the island's southernmost district after a burst of volcanic emissions. And it could generate ash plumes over an area 12 miles from the summit crater, the HVO said.
On Monday, the Hawaii State Department of Health warned residents in Lanipuna Gardens of risky levels of sulfur dioxide gas. "It's like a black, grimy soot".
Fissure No. 18 on Sunday also produced lava flow and fumes, Civil Defense officials said, raising fear of more evacuations. The eruptions have opened 20 vents in the ground, while lava has destroyed more than 40 structures, including two dozen homes.
Motorists are advised to drive with caution as metal plates will be placed over the cracks on the roadway, according to the agency.
Neal added that the receding lava lake resembles conditions seen before a major eruption in 1924, an explosion that killed one person and sent rocks, ash and dust into the air for 17 days.
Officials worry people in some areas with limited highway access could become trapped.
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