Government scientists have raised the alert level for the Mount St. Helens volcano in the northwestern U.S. state of Washington, saying the next eruption could threaten lives and property near the mountain.

Hundreds of visitors at an observatory eight kilometers from the volcano were asked to leave the area.

Scientists say pressure is building again inside the Mount St. Helens volcano following its first eruption in nearly 20 years.

The mountain quieted after spewing huge clouds of steam Friday. But by Saturday morning, scientists say energy releases were higher than they were before Friday's blast.

Mount St. Helens is remembered for its devastating explosion in 1980 that killed 57 people and covered towns hundred of kilometers away with ash. There was a smaller eruption in 1986.