A large explosion shook the Westhill neighborhood near Mount Vernon High School in Skagit County shortly after 6 a.m. Monday.

Firefighters arrived in the 900 block of East Fulton Street to find a residential structure engulfed in a blaze believed to have been fueled by a leaking natural-gas line, according to the Mount Vernon Fire Department.

Two people were inside the home when it exploded but escaped before the fire spread to the rest of the structure, the city of Mount Vernon said in a news statement Monday morning. One was taken to an area hospital; the other didn’t require medical attention, according to the city.

Gas was turned off in the area by 8:30 a.m., said Mark Hanson, a spokesperson for Cascade Natural Gas. The cause of the explosion is not yet known, but the utility company will work with the fire department to determine what happened, Hanson said.

Mount Vernon High School is closed Monday because of the fire and will resume normal hours on Tuesday, according to the school’s website.