(CNN) Hundreds of earthquakes in Hawaii are shaking the eastern side of the Big Island, and authorities are concerned that the Kilauea Volcano could erupt.

The US Geological Survey revised the magnitude of the most severe quake to a 5, from the 4.6 reported earlier. It hit at 10:30 a.m. local time on Thursday. Within half an hour, two more quakes came, registering at 2.5 and 2.7. There have been a total of six smaller earthquakes since the biggest one, the agency said.

County spokeswoman Janet Snyder said authorities have issued a mandatory evacuation order for a portion of Leilani Estates, a subdivision in the Puna District on Hawaii Island.

The frequency of the minor earthquakes decreased Thursday compared to the preceding days, the Hawaii County Civil Defense Agency said in a statement

However, the Hawaiian Volcano Observatory has indicated that a volcanic eruption was "possible but not imminent," the agency said.

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