Lava flowing from giant rips in the earth on the flank of Hawaii's erupting Kilauea volcano threatened highways, raising the possibility officials may order thousands more people to evacuate before escape routes are cut off.
Lava from a huge new fissure tore through farmland towards a coastal dirt road that is one of the last exit routes for some 2,000 residents in the southeast area of Hawaii's Big Island.
More lava-belching cracks are expected to open among homes and countryside some 40 kilometres east of Kilauea's smoking summit, possibly blocking one of the last exit routes, Highway 132.
Fountains of magma spouted "lava bombs" more than 30 metres into the air as the molten rock travelled east-southeast towards the coastal road - Highway 137 - the Hawaiian Volcano Observatory said.
Mass evacuations would be triggered if either highway is hit by lava, said Hawaii National Guard spokesman Jeff Hickman.
"There's a lot of worst-case scenarios and roads getting blocked is one of them," said Mr Hickman, standing on Highway 137, in the potential path of the lava flow.
Dozens of homes have been destroyed since eruptions began 10 days ago and officials have ordered the evacuations of nearly 2,000 residents in the lower Puna district of the Big Island, home to around 187,000 people.
The American Red Cross said 500 people sought refuge in its shelters on Sunday night because of worsening volcanic activity.
Two more fissures opened in the past 24 hours, bringing the total to 19.
"It's optimistic to think that this is the last fissure we're going to see," said Hawaiian Volcano Observatory deputy scientist-in-charge Steve Brantley. A similar seismic event in 1955 lasted 88 days, he said.
Unnerved by near-constant small earthquake tremors and emissions of toxic sulfur dioxide gas, Rob Guzman and his partner left their home in Kalapana Seaview Estates while they still could. "We just need the local government to calm down the panic that some of these 2,000 people are feeling, that today, we're going to be trapped with no way out," said Mr Guzman, who left behind a banana farm and rental properties to stay with friends.
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The Hawaii Fire Department issued a "condition red" alert on Monday because fissures in the southeast area of the Lanipuna Gardens area were issuing high levels of sulfur dioxide.
While residents deal with noxious gas and lava on the ground, the US Geological Survey is concerned that pent-up steam could cause a violent explosive eruption at the volcano crater, launching a 6,100-metre plume that could spread debris over 19km.
Scientists had expected such explosions by the middle of this month as Kilauea's lava lake fell below the water table. The possibility exists, however, that water may not be entering the crater, as feared, and gas and steam may be safely venting, scientists said.