The Kilauea volcano, the most active in Hawaii, was highly unstable Sunday as lava spouted into the air and fissures emitted deadly gases -- hazards that have forced thousands of people to evacuate.

Eight fissures have opened so far, the most recent one late Saturday, the Hawaiian Volcano Observatory reported at 9:40 GMT on Sunday.

All are in or near Leilani Estates and Lanipuna Gardens areas, where over 1,500 residents were ordered to evacuate.

The observatory, part of the US Geological Survey (USGS), said new crevices were spotted on Sunday morning but "no heat or escaping steam" was detected.

While lava continued to erupt intermittently in the Leilani Estates area -- with red-hot lava fountains sometimes spouting 230 feet (70 meters) into the air -- other eruptions have ceased.

But highly toxic sulfur dioxide gas pouring from some fissures continued to contribute to "extremely dangerous" conditions.

"The high levels of sulfur dioxide are a threat to all who become exposed," the Hawaii County Civil Defense office said in an alert.

That office reported Saturday that five houses have been destroyed. It said in a Facebook posting that "eruptive activity is increasing and is expected to continue."

The office cautioned Hawaiians to be patient. "Please understand the unpredictability of these hazards," it said.

Officials at Hawaii Volcanoes National Park, scene of a mandatory evacuation order Friday, were assessing roads and trails on Sunday as they weighed whether to reopen.

Civil defense administrator Talmadge Magno told the Honolulu Star Advertiser that some residents of the evacuated subdivisions might be allowed to return briefly to their homes to tend to animals and collect important papers. But, he cautioned, "We are pretty sure we are not done."

The area has suffered several severe shocks since Thursday, when a magnitude 5 earthquake under Kilauea's south flank set off an initial eruption. A quake Friday was measured at magnitude 6.9, the most powerful to hit the islands since 1975.

In a 48-hour period, experts detected 152 quakes of magnitude 2 to 3 and 22 of magnitude 3 within three miles (five kilometers) of the volcano's crater.

The observatory said satellites had detected a gradual sinking of ground around the volcano summit in the two weeks before the first quake.

It said the surface of a lava lake in the Overlook crater had dropped 518 feet (128 meters) below the crater rim since April 30.

Kilauea, which rises to 4,091 feet (1,247 meters), began erupting Thursday afternoon local time (02:45 GMT Friday).

Kilauea -- which according to Hawaiian folklore is home to Pele, the volcano goddess -- saw nearly continuous activity during the 19th century. It is one of five currently active volcanoes on Hawaii Island, sometimes known as the archipelago's Big Island.

"Kilauea ranks among the world's most active volcanoes," according to the USGS, "and may even top the list."