HAWAII VOLCANOES NATIONAL PARK, Hawaii (AP) -- Lava began bubbling Monday through the crust of one of the world's most active volcanoes -- Kilauea, on Hawaii's Big Island.

The eruption was confined to the volcano's summit caldera, in a remote, closed area of Hawaii Volcanoes National Park, the Hawaii Volcano Observatory reported. Increased earthquake activity began at about 2 a.m. local time and within about half an hour webcam images began to show lava emerging through fissures in the caldera or spurting in fountains.

The most immediate threat was from volcanic smog that could reach homes downwind, the observatory said. Such "vog" contains sulfur dioxide and can worsen symptoms for people who have conditions like asthma, other respiratory issues or cardiovascular disease.

The area where the eruption is occurring has been closed to the public since 2007 due to hazards that include crater wall instability, ground cracking and rockfalls.