The Hawaii community hardest hit by the Kilauea Volcano was ordered sealed off under a strict new mandatory evacuation as the eruption marked its fourth week with no end in sight.

The Big Island's mayor, Harry Kim, declared a roughly 17-block swath of the lava-stricken Leilani Estates subdivision off-limits indefinitely and gave 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.

At least 75 homes -- most of them in Leilani Estates -- have been devoured by streams of red-hot molten rock creeping from about two dozen large volcanic vents, or fissures, that have opened in the ground since Kilauea rumbled back to life four weeks ago. Lava flows also have knocked out power and telephone lines in the region, disrupting communications.

Besides spouting fountains of lava around the clock, the fissures have released high levels of toxic sulfur dioxide gas on a near constant basis, posing an ongoing health hazard. Meanwhile, the main summit crater has periodically erupted in clouds of volcanic ash that create breathing difficulties and other problems for residents living downwind.

The heightened volcanic activity has been accompanied by frequent earthquakes, as magma -- the term for lava before it reaches the surface -- pushes its way up from deep inside the earth and exerts tremendous force underground.

After a month of continual eruptions at Kilauea's summit and along its eastern flank, geologists say they have no idea how much longer it will last.