A stream of lava threatened to block a key Hawaii highway on Saturday (May 19) that serves as an escape route for coastal residents, while the first known serious injury was reported from fresh explosive eruptions from the volcano.

As magma destroyed four more homes, molten rock from two huge cracks merged into a single stream, threatening to block escape routes. It was expected to hit Highway 137 overnight if it kept up its rate and direction of flow, the County of Hawaii’s Civil Defense Agency said.

Authorities are trying to open up a road that was blocked by lava in 2014 to serve as an alternative escape route should Highway 137 or another exit route, Highway 130, be blocked, Jessica Ferracane of the National Park Service told reporters.

The park service is working to bulldoze almost a mile (1.6 kilometers) of hardened lava out of the way on nearby Highway 11, which has been impassable, she added.

The Hawaii National Guard has warned of mandatory evacuations if more roads become blocked.