PAHOA, Hawaii - A large explosion in Hawaii's Kilauea volcano on Wednesday may mark the beginning of more violent, explosive eruptions that could spray rocks for kilometers and dust nearby towns in volcanic ash and smog, the US Geological Survey said.

The USGS warned that more violent eruptions at the crater could begin in mid-May, shooting rocks weighing several tons for over half a kilometer, hurling pebble-sized projectiles several kilometers and dusting areas up 32 km away with ash.

"This is the first of perhaps more events like that to come," Tina Neal, the scientist in charge of the USGS Hawaiian Volcano Observatory, said of Wednesday's blast which shot projectiles from the crater.

The town of Hilo about 40 km northeast of Kilauea on Hawaii's Big Island and the village of Pahoa 39 km east, could be exposed to volcanic air pollution, or so-called vog, and a layer of ash should explosive eruptions begin and prevailing wind directions shift, Neal said.

Geologists cautioned that Kilauea's past explosions had been relatively small on a global scale, and while ash from the volcano posed a nuisance as an eye and respiratory irritant, it was not a serious health hazard. "We don't anticipate there being any wholesale devastation or evacuations necessary anywhere in the state of Hawaii," said Donald Swanson of the Hawaiian Volcano Observatory.

Hawaii County Civil Defense said all 1,900 residents of the Leilani Estates and Laipuna Garden areas, around 40 km east of the crater, had been evacuated. Lava oozing from two new fissures in the area had paused but sulfur dioxide gas was still a hazard.

Exposure to very high levels of the gas, which causes acid rain, can be life-threatening, according to the Agency for Toxic Substances and Disease Registry.

Fifteen fissures have opened since Kilauea's vents started spraying fountains of lava up to 90 meters into the air on Thursday and 47 hectares of land have been covered with lava.

Kilauea has been in a state of nearly constant eruption for 35 years. It predominantly blows off basaltic lava in effusive eruptions that flow into the ocean but occasionally experiences more explosive events.

Reuters