TIANJIN- At least 21 firefighters have died in the line of duty as of Friday afternoon after two massive explosions, on Wednesday, ripped through a warehouse in northern Chinese port city of Tianjin.

This could be the highest death toll of a rescue mission for firefighters since the founding of the People's Republic of China in 1949.

As of Friday, 56 people had died and more than 720 people had been hospitalized, including 25 critically wounded and 33 in serious condition, according to the rescue headquarters.

Local authorities have explained why the death toll of firefighters is so high.

"When the blast occurred, several firefighters were working to put out the fire, and backup forces had just arrived. They were caught off guard, so the casualties are grave," said Zhou Tian, head of Tianjin's fire department at a press conference on Friday.

"It was complete darkness [and] my buddies were badly injured," said one firefighter who managed to escape.

Firefighter Zhou Ti, 19, on Friday morning became the first and only firefighter to be pulled alive from the scene. The first words he uttered after regaining consciousness were: "Have the flames been put out?"

More than 1,000 firefighters have been dispatched to contain the raging fire, many of whom are in their 20s.

"If I don't make it, please take care of my dad," one firefighter wrote in a message to his friend before arriving at the blast scene. He returned home safe and sound, according to media reports.

Emergency response efforts were suspended temporarily on Thursday to avoid further casualties while military specialists arrived to investigate the extent of contamination from the dangerous chemicals that had been kept at the warehouse.