Scores of people living near the volcano's Halemaumau summit crater have already been evacuated.
A USGS statement said: "Ash emission from the Overlook crater within Halemaumau has generally increased this morning to previous days". Lava has burst from 21 giant ground cracks or fissures and torn through housing developments and farmland, threatening two highways that are exit routes for coastal areas.
The Hawaii Fire Department reported unsafe air quality around fissures in the southeast section of Lanipuna Gardens and surrounding farm lots on Pohoiki Road.
Since May 3, residents of Hawaii's Big Island have been struggling with the fallout from the recent and ongoing eruption of the Kilauea volcano.
The Hawaiian Civil Denfense Agency said: "Severe conditions may exist such as choking and inability to breathe". The gases are especially risky for the elderly, children, babies and people with respiratory problems, officials said. In an alert sent to those residents Monday afternoon, they were urged to leave the area.More news: Honor 10 First Look: Design, Camera, and More
A new fissure opened up today, fissure 19. The latest fissure is by the Lanipuna Gardens.
"It sounded like hammers in the dryer", she said. "When the sulfur dioxide hit my lungs once, it took my breath away". The eruption has destroyed 25 homes and covered 115 acres in lava.
Residents around PGV's Pohoiki power plant have anxious that earthquakes or a lava flow could cause an uncontrolled blowout that would spew toxic gases into their communities.
Scientists had expected such explosions by the middle of this month as Kilauea's lava lake fell below the water table. The observatory also warned that the eruption could become more violent.
Janet Babb, a geologist from the volcano observatory, said phreatic eruptions are "notoriously hard to forecast, and can occur with little or no warning".