Rain fell Wednesday on a red-hot river of lava as it threatened to consume its first home on its slow advance into a rural Hawaii town.

A breakout of the lava flow was about 30 metres from a Pahoa residence - about the length of a basketball court, said Hawaii County Civil Defense Director Darryl Oliveira. The couple who lives in the home has left.

Scientists from the Hawaiian Volcano Observatory who are walking alongside the lava reported its leading edge was 219 metres from Pahoa Village Road, which goes through a commercial hub of the Big Island's sprawling and isolated Puna district.

The leading edge remained in a large agricultural parcel that included another house, which was about 91 metres from the lava, Oliveira said.

Dozens of homes, business and other structures are in the area of the lava flow. That amount could increase as the flow front widens.

So far lava has burned a garden shed, tires and some metal materials.

On Wednesday, it burned mostly vegetation, while the rain helped tamp down smoke from the crackling stream.

Officials are monitoring hazards from the smoke. Chemists from the observatory detected only low levels of sulfur dioxide, Oliveira said.

The lava flow emerged from a vent in June and until recently had been slowly weaving through uninhabited forest and pastureland.

Jeff and Denise Lagrimas packed up to leave for a town 14 miles (22 kilometers) away. The flow is expected to slither past properties across the street from their home as it works its way toward the ocean, about 6 miles (9 kilometers) away. They decided not to stay and see if that happens or if the lava burns their home.