The Big Island's mayor, Harry Kim, declared an area around the lava-stricken Leilani Estates subdivision off-limits indefinitely, giving any residents remaining there 24 hours to leave or face possible arrest.
The mandatory evacuation zone lies within a slightly larger area that was already under a voluntary evacuation and curfew.
Civil defense officials have previously said about 2,000 residents in and around Leilani Estates were displaced at the outset of the current eruption, which began on May 3.
But the total number of evacuees was estimated to have risen to about 2,500 after authorities ushered residents from the nearby Kapoho area as a precaution on Wednesday, as a lava flow threatened to cut off a key access road.
Around 80 homes have been devoured by streams of red-hot molten rock from about two dozen large volcanic vents, or fissures, that have opened in the ground since Kilauea rumbled back to life four weeks ago.