TIANJIN — Rescuers pulled out a firefighter who was trapped for 32 hours after responding to a fire and huge explosions in the Chinese port city of Tianjin as authorities dealt Friday with a fire still smoldering amid potentially dangerous chemicals.

A rapid succession of explosions late Wednesday — one equal to 21 tons of TNT — killed at least 56 people, injured more than 720 and left several firefighters missing.

They were sparked by a fire at what authorities said were shipping containers containing hazardous material at a warehouse, and they struck a mostly industrial zone late at night — otherwise the death toll could have been much higher. But the warehouse was close enough to residences to appear out of compliance with safety regulations, raising questions about whether the facility had properly been authorized.

The toll included at least 21 firefighters among the more than 1,000 sent to the disaster. Firefighters initially responded to a fire at the warehouse and many of them apparently were killed by a series of explosions triggered 40 minutes after the fire was reported.

Zhou Ti, a 19-year-old firefighter, was pulled from the zone at about dawn Friday and taken to a hospital, where he was treated for face, chest and foot injuries, state broadcaster CCTV reported.

From his hospital bed, Zhou told CCTV the fire was spreading out of control. “I was knocked onto the ground at the first blast,” recalled Zhou, his eyes closed. “I covered my head and don’t know what happened after that.”

Tianjin Fire Department head Zhou Tian said at a news conference Friday that the explosions occurred just as reinforcements had arrived on the scene and were just getting to work.

“There was no chance to escape, and that’s why the casualties were so severe,” the fire head said. “We’re now doing all we can to rescue the missing.” Zhou Tian and Zhou Ti are not related.

The rescue of the young firefighter was a bright moment in a day otherwise clouded by mistrust and unanswered questions. Local officials have been hard-pressed to explain why authorities permitted hazardous goods warehouses so close to residential complexes and critical infrastructure. They also have been publicly reticent about suspicions that firefighters may have sparked the explosions by spraying water on volatile chemicals.

Hazardous chemical warehouses must be at least 1,000 meters (3,300 feet) away from public buildings, highways, railways and industrial enterprises under regulations enacted by China’s State Administration of Work Safety in 2001.