Hawaii's Big Island has declared a state of emergency as lava from an active volcano threatens nearby homes, which could be evacuated within days, officials and reports said Friday.

Hawaii County Mayor Billy Kenoi signed a proclamation Thursday after the lava flow from the Kilauea volcano advanced to within a mile of a residential area known as the Ka'ohe Homesteads.

"We are taking this step to ensure our residents have time to prepare their families, their pets, and their livestock for a safe and orderly evacuation from Ka'ohe in the event the flow continues to advance," Kenoi said.

The emergency proclamation lets authorities close roads to non-residents, to make it easier for people who live there to evacuate rapidly if necessary, said Hawaii County Civil Defense Administrator Darryl Oliveira.

No evacuation has yet been ordered, but residents are being urged to "finalize their evacuation plans and monitor county Civil Defense updates closely in the days ahead," said a statement from the mayor's office.

According to the Honolulu Star newspaper, the lava flow could reach houses within days, possibly a week.

Hawaii Island, or the Big Island, is the largest of the eight main islands which make up the Pacific US state -- an archipelago that includes hundreds of smaller volcanic islands.