BOULDER - Two people have been questioned and two more are in a burn unit at the University of Colorado Hospital after a house explosion in Boulder that police believe is drug-related.

The explosion happened at home near Chambers road and Broadway after 8 p.m. Thursday.

A neighbor told 9NEWS she heard a big boom and then her whole house shook.

"Everyone was kind of freaked out for a second,” said Faith Anderson, who lives nearby. “We could hear our neighbors yelling, ‘we need a fire extinguisher, we need a fire extinguisher.’ She was already on the phone with the cops asking for the fire department to come because there was a fire.”

Anderson told 9NEWS her entire family came out of the house after they heard the noise hoping to help.

“Then people came running out of the side of the house,” she said. “Very freaked out, the lady was looking at her hands like she was burned, she was just screaming over and over again that she needed to get to the hospital.”

Boulder police said the woman at UCHealth was in stable condition Friday, and the man was in the ICU.

Anderson said there is one thing she heard and saw that seemed even stranger than the explosion across the street from her home.

“When the owner of the house - was on the phone she was really freaked out and then all of a sudden she started back peddling like, 'no we’re fine, we don’t need anybody to come,'” Anderson said. “It was strange, I guess, because we all knew there was at least a fire started from something. To see her be so frantic, so scared that her house was going to burn down.

"Just to be all of a sudden, 'no, no don’t come.’ makes you wonder what else was happening inside that house.”

Boulder police said no one has been arrested.

9NEWS left messages for the two people listed as living in the home, including the homeowner, but haven’t heard back.