Two firefighters were killed after a warehouse collapsed in Baoshan district over the Spring Festival holiday, the local fire department said Thursday.

The two firefighters, Lu Chen, 23, and Sun Luoluo, 19, were putting out a fire inside a warehouse at a packaging material factory when the building unexpectedly collapsed, trapping them and two other firefighters from the squad, according to a post on the Baoshan district fire department's microblog.

Sun was found dead on scene. Lu died after being rushed to a nearby hospital, the post said. 

The fire broke out around 10:50 am Tuesday. Eleven firefighting teams and 30 fire engines were dispatched to the scene. They got the blaze under control around 1:10 pm.

A squad of four firefighters, including Lu and Chen, entered the warehouse afterward to put out any remaining flames inside. The building collapsed while the squad was on its second round through the building.

Sun was found dead beneath 10 meters of debris around 5 pm. Lu was found around 2 pm.

The other two firefighters were injured, the post said.

Nearby residents said they heard the sound of firecrackers going off around 9 am, the Oriental Morning Post reported.

The Baoshan district government told Shanghai Television Station Thursday morning that an investigation into the fire was underway.