Baku, May 4, AZERTAC hangA poisonous cloud is hanging over Berlin after a chemical factory blaze, with firefighters warning deadly hydrogen cyanide could develop, according to Daily Mail. Firefighters said sulphuric acid and copper cyanide were stored at the plant and the chemicals ignited, which could create hydrogen cyanide.People were warned to close all windows, stay inside and switch off ventilation units after the fire hit the firm. The state of Berlin has issued an official danger warning and urged people to stay away from the area as the cloud of smoke is already spanning over nearly all of the western area of the city.The blaze is at Diehl Metal Applications in Berlin's Lichterfelde district, which is a sister company to the Diehl Defence concern, manufacturer of the deadly IRIS-T missiles.Diehl Defence has its headquarters on the same street as the burning building. Diehl Metal Applications reportledy operates its own electroplating system for refining metal surfaces in the building that is on fire. 'The building is now completely burned through on four floors. Part of the building has already collapsed,' Adrian Wenzel, spokesman for the Berlin fire department and on site at the scene of the fire, told German tabloid Bild. He added: 'We are only trying to put out the fire from the outside. The fire can no longer be brought under control from the inside.'Local outlet Berliner Zeitung reported several detonations being heard on site. There are currently 190 firefighters at the site, wearing protective suits. Students and teachers from nearby schools have been sent home as a precaution and several shops in the area have also closed. There is no currently no information available on the cause of the fire, but the spokesman for the fire department said there have been no injuries reported. The operation to get the fire under control is expected to last into the night after firefighters have been struggling to bring it under control since it broke out around 10.30am local time. Parts of the building have reportedly collapsed.