Lava from a vent in Kilauea Volcano on the Big Island of Hawaii began flowing into the ocean 7 miles (11 km) away on Saturday. The volcano has been erupting continuously from its Pu'u O'o vent since 1983.

The flow was the first from the volcano to reach the ocean since December, said Janet Babb, spokeswoman for the U.S. Geological Survey's Hawaiian Volcano Observatory.

Even as Hawaii tourism officials awaited an increase in visitors drawn by the explosive natural show, officials warned of potentially deadly risks and urged visitors to stay a safe distance away and respect barriers placed around the lava flow.

"Ocean entries can be quite beautiful but also quite dangerous," Babb said.

When the lava reaches the ocean, it cools, darkens and hardens into a lava delta amid an outpouring of steam. The lava delta is newly created land that is unstable and can collapse without warning.

When it collapses, even visitors standing 100 yards (metres) away can be hurt because large chunks of lava and hot water are hurled their direction by the collapse, Babb said.

"The molten lava meeting the ocean creates steam which may look innocuous, but can be quite hazardous," she said. "It's acidic and contains tiny particles of volcanic glass. And waves crashing with the lava can send out scalding water."

It was not clear how long the lava would continue flowing into the ocean.

George Applegate, director of the Big Island Visitors Bureau, said he expected an increase in tourists due to the latest occurrence of the phenomenon. "We always do," Applegate said. "A lot of people want to see a live lava flow."

Tourism officials declined to estimate how many more visitors they might see on the Big Island because of the lava flow. Hawaii Volcanoes National Park, which encompasses Kilauea, welcomed more than 1.3 million visitors last year, according to park spokeswoman Jessica Ferracane.

Security workers were keeping people beyond the barriers during approved viewing hours, said Barry Periatt, plans and operations officer for Hawaii County's Civil Defense Agency.

No communities around the volcano are threatened by the lava flow, Periatt said. The nearest town is Kalapana Gardens, which is more than half a mile (1 km) away. It suffered major damage from a 1986 volcano flow. (Editing by Alex Dobuzinskis, Cynthia Johnston and Mohammad Zargham)

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