HONOLULU: A section of sea cliff above a massive "firehose" lava flow on Hawaii's Kilauea Volcano has collapsed and splashed into the ocean as tourists and geologists watched.

A large crack in the section of cliff above the gushing molten lava stream gave way Thursday afternoon as scientists stood just yards away. Geologists with Hawaii Volcano Observatory were at the site to monitor the crack when it collapsed and captured the scene on video .

Later in the day, a tour boat was cruising by when another section of the cliff collapsed. Video shows guests gasping and screaming as the huge piece of land splashes down in front of them, sending debris high into the air.

The collapse stopped the heavy stream of lava that had been arching out from near the top of the cliffs for weeks. The lava stream, dubbed a "firehose" flow because it shoots lava outward from the source like water from a hose, had recently increased in intensity.

The massive Kilauea flow came from a lava tube at the Kamokuna ocean entry on the southeast side of the Big Island.

The lava was gushing from a tube that was exposed when a huge, 26-acre lava rock delta collapsed into the ocean at the site on New Year's Eve. That collapse triggered massive explosions and giant waves in the area.

The USGS warned that a portion of unstable cliff may still be attached and could break off at any time.

"This collapse yesterday did not diminish the hazards," said USGS geologist Janet Babb on Friday. "As long as lava continues to flow into the ocean, that area is still quite hazardous... there's still potential for collapses of the sea cliff there."

When the molten lava hits the cool seawater, it reacts and causes explosions that can throw large chunks of hot rock and debris inland, where tourists hike in to see the lava, and seaward, where tour boats cruise the shoreline.

The gasses released from the reaction are also dangerous to breathe, and shards of volcanic glass can be thrown into the air when the hot lava meets the cool seawater.

The National Park Service has set up a designated viewing area far from the flow where visitors can safely view the lava.

But some people cross lines and venture into closed, dangerous areas, officials said.

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