A red alert, according to the agency, means a "major volcanic eruption is imminent, underway or suspected, with hazardous activity both on the ground and in the air". The warning was raised to red - the highest threat level for aircraft - from the previous orange level (when volcanic ash emissions into the air are less serious) on Tuesday.
Coombs said the fissure had diminished in intensity, but officials said activity can go up just as quickly as it goes down.
See more photos of the massive ash plume below.
The observatory warned the eruption could become more violent. "Avoid excessive exposure to ash which is an eye and respiratory irritant". It can make roads slippery, clog drinking water catchment systems common on the island and cause the failure of electrical power lines in large enough quantities, said USGS chemist David Damby.
At least that is what happened at the appropriately named Volcano Golf & Country Club this week, with a volcano on the island of Hawaii, forcing mass evacuations.
Ash cloud from Hawaii's Kilauea volcano sparks red alert for aircraft
As a result, officials announced most of Hawaii Volcanoes National Park would be closed indefinitely to keep visitors and park employees at a safe distance from a possible eruption.
"Things seem to be progressing largely as they have been, except for a shift in wind and less ash", Poland said.
In a statement, the USGS said: "As of early this morning, eruption of ash from the Overlook vent within Halemaumau crater at Kilauea Volcano's summit has generally increased in intensity".
Besides the ash, which is not poisonous, residents have to worry about choking on sulfur dioxide.
The explosive, steam-driven eruptions could drive a 20,000-foot (6,100-meter) ash plume out of the crater, hurl boulders the size of small cars up to half a mile (800 meters) and scatter smaller rocks over 12 miles (19 km), the USGS has warned.
There have been no major injuries or deaths reported from the eruption.
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