What we need to know

Massive explosions at a chemical storage facility in one of China's biggest cities this week killed at least 56 people and injured 700. They also raised fears about toxic chemicals poisoning the air. Here are a series of questions and answers explaining what is known about the blasts, but also the fears over a lack of information about the chemicals that may have been dispersed.

How did the explosion occur?

Two massive explosions took place about 11:30pm, with the blasts so powerful that they damaged buildings several kilometres away. Authorities have given no reason for the fire, or how it led to the explosions. Authorities have also said they do not know what exactly was stored at the facility, although the company's business was in dealing with a host of extremely dangerous chemicals.

How many casualties and who were they?

At least 21 of the 56 people confirmed killed were firefighters who came to tackle the initial blaze. Many others were migrant workers who lived in dormitories nearby. More than 700 injured were hospitalised, 70 of whom were still in critical condition yesterday, according to Xinhua. Eighteen firefighters remained missing, it said.

What was the extent of the damage?

Residents likened the shockwaves to an earthquake, and buildings three kilometres away had their windows shattered. About 10,000 new imported cars near the blast site were destroyed, according to Chinese media reports, rows upon rows of shipping containers crushed, and buildings reduced to burnt-out shells. Even a kilometre away, building facades were damaged and showed burn marks. Up to 6,000 people were relocated on Thursday to schools because their homes were damaged by the shockwaves, according to Xinhua.

What has been the government's response?

Authorities have struggled to completely extinguish the blaze, which was still smouldering yesterday morning, and determine exactly what was in the storage facility. They have also moved to limit criticism of handling of the disaster, blocking some critical posts on social media. Executives from the company that ran the storage facility, Tianjin Dongjiang Port Rui Hai International Logistics were quickly detained on Thursday. Firefighters and other rescue workers have continued to search for dozens of people still missing. One missing firefighter was pulled out alive from the debris on Friday morning.

What are the concerns now?

That extremely dangerous chemicals could be floating in the air, may still be leaking from the facility or could cause another explosion. Chinese authorities have given mixed signals about the threat level. Chinese media said late Thursday that there were 700 tons of deadly sodium cyanide at the site, but those reports had by yesterday been pulled off newspaper websites. A military team of 217 chemical and nuclear experts were deployed to test the air for toxic gases, and rescue teams wore protective clothing in the blast area. An environmental expert told an official press conference yesterday that toxic gas indicators were now within normal limits and the air "should be safe for residents to breathe". However, Greenpeace released a statement saying chemicals stored by the company could react violently with water and cause more explosions.