A red alert has been issued for planes after explosions from Hawaii's Kilauea volcano intensified.
Ash and volcanic smog, or vog, as it is called, rose to 12,000 feet (3,657 meters) above Kilauea's crater and floated southwest, prompting an "unhealthy air" warning in the community of Pahala, 18 miles (29 km) from the summit.
An aviation red alert means a volcanic eruption is under way that could spew ash along aircraft routes, the US Geological Survey (USGS) says on its website.
Ash is not poisonous but irritates the nose, eyes and airways. It also makes roads slippery and large emissions can cause the failure of electrical power lines.
A shift in winds was expected to bring ash and vog inland and make them more concentrated.
"We're observing more or less continuous emission of ash now with intermittent, more energetic ash bursts or plumes," Steve Brantley, a deputy scientist in charge at the Hawaiian Volcano Observatory (HVO), said.
The observatory warned the eruption could become more violent.
"At any time, activity may become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent," the HVO said in a statement on the change in aviation alert level from orange to red.
The news of the alert comes as a giant new fissure blasted ballistic rock and "lava bombs" more than 100 feet (30 metres) into the sky.
Measuring about 1,000 feet (300 metres) long, lava from the huge crack also tore through farmland towards a coastal dirt road – one of the last exit routes for around 2,000 residents in the southeast area of Hawaii's Big Island.
Hawaii County Civil Defence issued an emergency alert after the fissure was discovered and officials called for more evacuations as fears grew about a potential major eruption at volcano's summit.
More fissures are expected to open among homes and countryside some 25 miles east of Kilauea's smoking summit, possibly blocking one of the last exit routes, Highway 132.
Agencies contributed to this report