Four people were injured on Thursday afternoon after an explosion at a chemical factory in Main Rain Reef Road in Boksburg, Johannesburg."We had one patient seriously burnt in the face, head and neck [who] has been taken to Glenwood hospital for treatment," Ekurhuleni Emergency Services (EES) spokesperson William Ntladi said.He added that three others were also taken for treatment for serious body burns and smoke inhalation.CHEMICAL FACTORY ON FIRE : MAIN REEF CNR KENT. DUNSWART. BOKSBURG. EMM. GP. AVOID!!! pic.twitter.com/6u8i7lFfHP— REZA (@crimeairnetwork) November 8, 2018Ntladi said they have not yet established what caused the chemicals to explode."The information is not yet clear, but we know that some chemicals do react to each other and can cause [an] explosion. But that will be investigated by the relevant authorities," he said.He added that it was alleged that there was a chemical reaction.Ntladi said sulphuric acid, hydrochloric acid and many other substances were in the area that could have caused the explosion. Five fire engines and about 25 firefighters were on the scene and the blaze has since been contained. "We are busy cooling off the hotspots," he said.Parts of the factory were completely destroyed.