A SERIES of explosions at a dangerous goods storage depot was thought to have killed 70 people and injured about 200 in Shenzhen yesterday and sent a fireball into the sky that was seen from Hong Kong. The explosions left a pall of potentially dangerous smoke hanging over Shenzhen and triggered a tremor which was felt here. The first explosion erupted at a warehouse for the Anmao Dangerous Goods Shipping and Storage Company at Qingshuihe Warehouse Zone at 1.35 pm, according to an early despatch from Xinhua (the New China News Agency). Witnesses said the blast occurred 10 to 15 minutes earlier. By 5.30 pm, eight of the 10 warehouses in the zone had exploded in succession. Xinhua gave no death toll in its despatch but said more than 100 people had been killed or injured, many of them firefighters, policemen and medical workers. One worker fleeing the blast said: ''It was like an atomic bomb exploding. Hot currents were racing up to the blackened sky after the blast.'' The Hong Kong China News Agency (HKCNA) said a release of ammonium nitrate sparked the first blast, which destroyed a warehouse storing fireworks and matches. Firefighters and police rushed to the scene and were trying to control the blaze when a nearby natural gas reservoir, Shenzhen's largest, exploded. The news agency said some 70 people, including two deputy police chiefs, were feared dead in the accident. It was described by officials as the worst in the history of the border city. It said the Red Cross hospital in Shenzhen alone had already admitted about 200 people. A Hong Kong Government spokesman said last night ''urgent preparations'' were being made by essential services to assist with firefighting and rescue work. Troops would be sent to assist with rescue efforts if requested by the Shenzhen authorities, a spokesman said. The Director of Fire Services, Gerry Lam Chek-yuen, flew to Shenzhen with two senior officers to make an on-the-spot assessment. Their helicopter landed on the roof of a 53-storey building in the centre of the city and they later held discussions with Chinese officials before being taken to the depot. When he returned early this morning, Mr Lam said three or four helicopters of the Government Flying Service will fly to Shenzhen today to water bomb the fire. A senior officer will travel to Shenzhen this morning, to co-ordinate the water bombing mission from the ground. Mr Lam said although the Shenzhen authorities have enough medical and manpower resources, they lacked adequate water supplies and requested help in supplying additional water to fight the blaze. The Shenzhen fire brigade was still battling to extinguish the blaze late last night and officials had not ruled out the possibility of further explosions. Authorities appealed for residents not to use any water until the fire had been put out. Supplies were having to be transported to the site from many kilometres away. Mr Lam described the affected area as twice the size of the Happy Valley racecourse. He said that as far as he is aware, three Public Security Bureau officers had been killed and 25 bureau personnel and ''many firemen'' had been injured. ''If this fire was in Hong Kong, I would classify it as a disaster.'' The Shenzhen city authorities set up two 24-hour hotlines (557 2250 and 557 1044) for families to get details of injured relatives and to provide assistance for those who had suffered in the blasts. The HKCNA said an emergency command team led by vice-mayor Wang Zhongfu and deputy party committee head Lin Zuji had been formed to oversee the rescue operation. One team member, vice-mayor Li Chuanfang, ordered the deployment of trains and container trucks to remove the remaining gas cylinders from the scene and transport them to safer sites. Municipal officials said they were investigating the cause of the explosions and whether owners of the warehouses had violated laws on the storage of dangerous goods. The semi-official China News Service said last night the blaze was ''basically under control'', but added that the number of casualties was still being counted. According to the HKCNA, the two main explosions occurred at about 1.25 pm and 2.30 pm at the warehouse, which is 30 minutes' drive from Lowu. The first explosion was caused by ammonium nitrate in a storehouse operated by the Shenzhen Anmao Company, which was said to be run by the Chinese military, according to HKCNA. Officials from all major rescue departments were deployed. But an hour later the scorching heat from the first explosion ignited a second, and more intense, blast at the gas storage plant. The area was cordoned off for a distance of two to five kilometres and city traffic was brought to a standstill. Huge mushrooms of black smoke billowed from the site and could be seen at the border area of Hong Kong and at Fanling. Hong Kong's Royal Observatory said it recorded earth tremors after the second explosion. Some residents in the Special Economic Zone living several kilometres from the site said they felt the tremor of the explosions. Furniture was shaken and windows broken in shockwaves from the blast, they said. One worker at the Shen Chang Oil Company, about 200 metres away from the scene, said the situation was chaotic. ''We were working at our oil depot, which was not damaged. When the second explosion occurred, we immediately dived on to the floor and later ran out of the depot. ''The situation was chaotic and there was a big fire after the explosion. We managed to run out before police and firemen sealed off the scene,'' she said after arriving in Shenzhen. Two deputy heads of the Public Security Bureau in the city, Yang Shuitong and Huang Jingfan, died at the scene. Several public security officers, armed police and firemen were also reported injured. A journalist from the Shenzhen Television Station, Dai Jie, was also hurt and sent to hospital for treatment. Another reporter from the Shenzhen Special Economic Zone Herald fell to the ground after being hit by the huge air-current caused by the explosion. The HKCNA report quoted unconfirmed sources as saying the death toll could reach 70, most of whom were hit by the second explosion. It said all major hospitals in the city were working at full strength to cope with the large number of injured. A spokesman at the Shenzhen People's Hospital said they had enough manpower to cope. A Shenzhen government spokesman, Huang Xinhua, said the explosion was the worst in the city's history. ''The municipal government is extremely concerned about the incident. A special team has been formed by the Public Security Bureau, armed police and medical staff to conduct the rescue operation.'' Mr Huang said it would conduct an investigation into the cause of the explosion and whether the owners of the dangerous goods storage area had broken the law.