TIANJIN, Aug. 15-- Massive blasts in a Tianjin warehouse have dealt a hard blow to north China's trade and logistics hub, disrupting businesses and displacing thousands.

Explosions destroyed the warehouse in Tianjin Binhai New Area on Wednesday night, leaving at least 56 people dead, including 21 firefighters. Another 721 were hospitalized, according to rescue headquarters.

"After the first blast, firefighters [on the scene] were caught off guard by a second explosion, so the casualties are grave," Zhou Tian, head of the city's fire department, told a press conference on Friday.

More than 1,000 firefighters and 140 fire engines were deployed. The fires are almost completely out and 44 people have been rescued, he said.

One 19-year-old firefighter was pulled out alive more than 30 hours after the catastrophe. He is in hospital in a stable condition.

No flames were visible at the core area of the blast site, but dark smoke still billowed from the vast area of devastation, where charred, smoldering shipping containers tower more than 20 meters in the air.

Four sensors have been placed in the "core blast zone" to detect toxic gas, said Wang Dongsheng, director of the nuclear and chemical forces of the Beijing military area.

Twelve schools and three apartment buildings are being used to to accommodate 6,300 people displaced by the blasts.

At Tianjin Armed Police Medical College Affiliated Hospital, 11 psychologists offer counseling to patients with post traumatic stress.

"One firefighter, who narrowly escaped being killed, sees fire and dying people whenever he closed his eyes," said psychologist Wang Yuping.

ECONOMY MAY SUFFER

The blasts are expected to drag down the booming growth of Binhai New Area, a flagship industrial park that made Tianjin one of China's fastest growing areas.

The catastrophe has affected 17,000 households and 1,700 enterprises, according to Zhang Ruigang, vice head of the new area.

Binhai's economy could face downturn pressure on trade and logistics industries in the third quarter, said Tang Zhongbin, director of the planning office of the area's development and reform commission.

Making up 55 percent of Tianjin's GDP, the area recorded economic growth of 15.5 percent growth last year, mainly supported by aviation, auto, IT, petroleum and chemical engineering.

Tianjin Port, a gateway to northeast China that processes about 40 percent of China's imported cars, could be hurt, according to the commission. Shipments of iron ore to the port have also been disrupted.

Auto makers who have warehouses close to the blast site were affected. Renault said it lost nearly 1,500 vehicles to conflagration. Volkswagen has temporarily suspended logistics and transportation of vehicles at the port, moving this arm of the business to Shanghai and Guangzhou.

Four aircraft at a heliport, 1,100 meters away from the site, were destroyed and the hangar's door was ripped off and staff were wounded.

Express delivery services have also been seriously delayed.

Trains connecting downtown Tianjin and Binhai haves been suspended as Binhai Station was destroyed in the blast.

One of the world's fastest computers, Supercomputer Tianhe-1, was shut down for half an hour following the blasts as the building that houses it was damaged.

SAFETY CONCERNS

Pictures of grave destruction after the blasts have been widely shared on the Internet, sparking public outcry over the storing of dangerous chemicals in such close proximity to residential buildings.

The company had passed an environmental impact assessment that meant it was allowed to store dangerous chemicals. According to the assessment, 100 percent of the surveyed public believed the warehouse's location was appropriate.

Vanke, developer of one of the two communities damaged by the blasts, said when it obtained the land in 2010, the warehouse stored ordinary goods.

The developer said it had never been informed that the warehouse was now storing dangerous chemicals.

The warehouse is 560 meters away from the Vanke community and 630 meters from the former metro station.

Jin Xin, associate professor with Beijing University of Chemical Technology, believes the warehouse was too close to a residential area.

Since the investigation into the incident is still underway, it is too early to jump to conclusions.

The public is also concerned with the possibility of subsequent air and water pollution. Face masks and bottled water have been handed out.

Tianjin has set up 17 air- and five water-monitoring stations. Three sewage outlets to the sea have also been closed.

The air near the site was below a safe standard on Friday evening, forcing firefighters and one command headquarter to temporarily vacate the site.