TIANJIN, China -- New small explosions rocked a disaster zone in the Chinese port of Tianjin on Saturday as teams scrambled to clear dangerous chemical contamination and found several more bodies to bring the death toll to 104 in massive blasts earlier in the week.

Angry relatives of missing firefighters stormed a government news conference to demand any information on their loved ones, who have not been seen since a fire and rapid succession of blasts late Wednesday at a warehouse for hazardous chemicals in a mostly industrial area.

The death toll in the ensuing inferno included at least 21 firefighters -- making the disaster the deadliest for Chinese firefighters in more than six decades.

An unknown number of firefighters remain missing, and a total of 720 people were injured in the disaster in Tianjin, 120 kilometres (75 miles) east of Beijing. One additional survivor was found Saturday.

Two Chinese news outlets, including the state-run The Paper, reported that the warehouse was storing 700 tons of sodium cyanide -- 70 times more than it should have been holding at one time -- and that authorities were rushing to clean it up.

Sodium cyanide is a toxic chemical that can form a flammable gas upon contact with water.

Authorities also detected the highly toxic hydrogen cyanide in the air at levels slightly above safety levels at two locations in the afternoon, The Paper cited Tianjin environmental official Wen Wurui as saying. But the contamination was no longer detected later Saturday and there was no obvious impact on anybody in the area, the report said.

The disaster has raised questions about whether dangerous chemicals were being stored too close to residential compounds, and whether firefighters may have triggered the blasts, possibly because they were unaware the warehouse contained chemicals combustible on contact with water. The massive explosions Wednesday happened about 40 minutes after reports of a fire at the warehouse and after an initial wave of firefighters arrived and, reportedly, doused some of the area with water.

Authorities on Saturday pulled out one survivor from a shipping container, state media reported. His identity was not immediately known. Television video showed the man being carried out on a sketcher by a group of soldiers wearing gas masks.

Authorities were keeping residents, journalists and other people not involved in the disaster response outside a 3-kilometre (1.8-mile) radius around the site of the explosions in what media reports said was an operation to clean up the sodium cyanide.

Flames were spotted in the disaster area on Saturday, and explosions were reported by witnesses and state media.

In one case, heavy smoke from a fire engulfing several cars rose as high as 10 metres (yards), accompanied by at least five explosions.

Police and military personnel manned checkpoints on roads leading to the blast sites, and helicopters were seen hovering in the overcast sky. The air had a metallic chemical smell, and there was uneasiness over rain forecasts, although it was warm and windy.

Meanwhile, family members of missing firefighters disrupted the latest news conference about the disaster, demanding to know whether their loved ones were still alive.

"(The authorities) didn't notify us at all," said Liu Huan, whose son Liu Chuntao has been missing since late Wednesday. "Our son is a firefighter, and there was a team of firefighters who lost contact. We couldn't contact him."

Liu Longwang said she had not heard a word on her son Liu Ziqiao, also a firefighter. "We are extremely worried," she said. "He just turned 18."

State media reported that the casualties of the first three squads of firefighters to respond and of a neighbourhood police station have not yet been fully determined, suggesting that the death toll could rise further.

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 getting to work. "There was no chance to escape, and that's why the casualties were so severe," he said. "We're now doing all we can to rescue the missing."

One surviving firefighter, 19-year-old Zhou Ti, was found Friday morning and taken to a hospital. Zhou Ti and Zhou Tian are unrelated.

Li Yonghan, a doctor at Teda Hospital, called Zhou's survival "miraculous" and said Zhou escaped death mainly because he was covered by his fallen comrades. Zhou had massive injuries, including burns and leg cuts.

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

Lin Yujie, who lives in a nearby residential complex, said when he initially heard the blasts Wednesday night he thought they were a massive air strike.

"It was just a sea of fire," Lin recalled. "We were really worried that there would be a second or third explosion and what we would do then."

As details of the blasts and the rescue efforts surface, members of the public have been raising questions about whether fire commanders had erred in prematurely sending firefighters into a highly dangerous zone and using water to put out flames on the site known to have stored a variety of hazardous chemicals, including sodium cyanide and calcium carbide, which become flammable on contact with water.

Local officials also have been hard-pressed to explain why authorities permitted hazardous goods warehouses so close to residential complexes and critical infrastructure, clearly in violation of the Chinese rule that hazmat storage should be 1,000 metres (yards) away from homes and public structures.

Pope Francis, meanwhile, offered his prayers to the victims of the disaster. "I assure my prayers for those who lost their lives and for all those persons tried by this disaster," he said Saturday in remarks to thousands of people gathered in St. Peter's Square.

Francis made the remarks despite a tense relationship between Beijing and the Vatican.