The blaze broke out Tuesday morning at 12:30 at the Colonial Garden apartments in the 400 block of Plaza Boulevard in Morrisville.
Flames whipped through a basement unit of the complex, trapping two people inside.
Firefighters battled through the flames and smoke to pull them out.
They are in the hospital in serious condition with smoke inhalation.
Crews managed to contain the flames to the one unit.
Investigators are searching for the cause.
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