The Kilauea volcano on the archipelago of Hawaii in the United States spewed ash up to 12,000 feet in the air on Tuesday, prompting officials to warn residents to stay indoors and airplanes to stay away from the area, CNN reported.

“We have seen the waxing and waning [of volcanic activity over the past few days],” said Michelle Coombs, a geologist with the Alaska Volcano Observatory. “It seems that the system up at the summit has been what we call somewhat open, relieving that pressure. So, it intensified today but it was not the big one.”

The volcano might “plug up” if the magma level in the crater drops, thus allowing the pressure to build up, she added.

A few of the vents formed by the volcano are now releasing extremely high levels of sulphur dioxide, which is toxic and potentially life threatening. Winds are carrying the ash southwest of the volcano’s Halemaumau crater to towns such as Pahala, Wood Valley, Punaluu and Hawaiian Oceanview Estates, CBS reported. The ash could also affect crops and animals.

The volcano began erupting on May 3, and since then at least 20 lava fissures have opened up, destroying more than two dozen homes or structures. The lava has created a 3.21-km path heading towards the ocean. This has raised questions about accessibility to two highways that may have to be closed. In such a scenario, the one-lane beach road will be the only evacuation route, CBS reported.