Leverkusen - One person has died and four are missing after an explosion at a chemical park in western Germany, the site operator said on Tuesday, urging residents to stay indoors as a column of black smoke billowed from the area. Another 31 people were injured in the incident at the Chempark complex in the city of Leverkusen, according to police, five of them seriously.  The cause of the huge blast, which was heard several kilometres away, remains unknown. Germany’s NINA warning app sent an “extreme danger” alert to residents, telling them to close their doors and windows and keep emergency numbers free as much as possible. The explosion happened at around 09:40 am (0740 GMT) at Chempark’s waste incineration site in Leverkusen’s Buerrig district, according to site operator Currenta.