Four people flying in a hot air balloon over Southern California's wine country were hospitalized with burns after an explosion on board caused a crash-landing.

Riverside County Fire Department officials told the Associated Press that five people were in the balloon when a sudden blast ripped through the craft, causing it to crash into a field of vineyards near Temecula, Saturday morning.

Officials are still unsure of what caused the explosion, and can't specify whether the blast happened before or after the balloon hit the ground, AP reported.

One person sustained severe burns. Two other people were seriously injured, while one only had minor injures and another left the scene unscathed.

The identities of the people who were in the hot air balloon have not yet been publicized.

The National Transportation Safety Board has been tasked with a probe into the event, and told the Associated Press they've initiated an investigation into the incident, as they do with most crashes.

Residents and tourists alike often take hot air balloons in the area, located 60 miles north of San Diego. The view is scenic, and many enjoy soaring over the lush California greenery.

This is the first report of a hot air balloon accident in the area this year.