The blasts in the city of Tianjin on Wednesday night killed at least 50 people, including a dozen fire fighters, state media said. About 700 people were injured, 71 seriously.
The explosions at the port, the world's 10th largest, were so big they were seen by satellites in space and registered on earthquake sensors.
The warehouse was designed to store dangerous and toxic chemicals, according to an assessment by environmental inspectors published in 2014.
It was storing mainly ammonium nitrate, potassium nitrate and calcium carbide at the time of the blasts, according to the police.
A team from the International Atomic Energy Agency's Beijing environmental emergency response centre, as well as 214 Chinese military nuclear and biochemical materials specialists, had gone to Tianjin, the official Xinhua news agency said.
Several thousand residents were moved to 10 nearby schools after apartment buildings and homes were damaged, mainly by shockwaves from the explosions, it said.
Two fires were still burning late on Thursday.
Vast areas of the port were devastated, crumpled shipping containers were thrown around like match sticks, thousands of new cars were torched and port buildings reduced to burnt-out shells, Reuters witnesses said.
It said numerous other Japanese companies sustained minor damage to their operations.
French carmaker Renault said more than 1,000 of its cars were damaged but no staff were hurt.
Around 4,000 cars belonging to Hyundai Motor Co were at the site but damage had not yet been assessed, a spokesman said.
Mining giant BHP Billiton said its port operations and shipments were disrupted but its iron ore discharging berth had not been damaged.
Oil tanker arrivals and departures were also disrupted.
Xinhua said several containers had caught fire beforehand.
The state-run Beijing News earlier cited Tianjin fire authorities as saying they had lost contact with 36 fire-fighters.
By late afternoon, Xinhua reported 18 were missing, while 66 were among the hundreds of people being treated in nearby hospitals.
Anxious residents rushed to hospitals to seek news about injured loved ones. Dozens of police guarded the entrance of the TEDA hospital, a Reuters witness said.
The blasts shattered windows in buildings and cars and knocked down walls in a 2-km radius around the site.