WASHINGTON

Mauna Loa, the world's largest active volcano, began to erupt overnight, prompting authorities to open shelters "as a precaution" on Monday.

The volcano, located on Hawaii's Big Island, has not erupted since 1984 when it emitted lava for over three weeks.

Hawaii's Emergency Management Agency said it received reports of lava beginning to overflow along the southwestern part of the volcano's caldera, or the large hollow bowl at the top of the volcano.

Still, the agency said that there are not any current indications that lava is threatening populated areas, and noted that no evacuation orders have been issued.

Authorities have issued an ashfall advisory for the Big Island and surrounding waters. The National Weather Service is urging people with respiratory illnesses to remain indoors and avoid inhaling ash particles, and urging anyone who ventures outdoors to don a mask or cover their mouth and nose with a cloth.

"Possible harm to crops and animals. Minor equipment and infrastructure damage. Reduced visibility. Widespread clean-up may be necessary," it added.

The volcano began erupting at around 11:30 p.m. Sunday night inside Hawai‘i Volcanoes National Park, the Hawaiian Volcano Observatory said in an alert.

"Based on past events, the early stages of a Mauna Loa eruption can be very dynamic and the location and advance of lava flows can change rapidly," it said. "If the eruption remains in Moku‘āweoweo, lava flows will most likely be confined within the caldera walls. However, if the eruptive vents migrate outside its walls, lava flows may move rapidly downslope."