One person died and three were missing after an explosion rocked a chemical park in the western German city of Leverkusen on Tuesday, officials said, but a warning for residents to stay indoors was lifted several hours later.
Another 31 people were injured in the incident at the Chempark complex, three of them seriously, city authorities said in a statement. All those affected worked at the site.
The cause of the huge blast, which was heard several kilometres away and sent a column of black smoke into the air, was not immediately clear.
Germany's NINA warning app sent an "extreme danger" alert to residents, telling them to stay home and shut doors and windows.
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.
The site is separate from the main industrial park nearby that houses numerous chemical companies including Bayer, Lanxess and Evonik Industries.
"I heard the terrible bang and immediately closed doors and windows, we live near Chempark after all," tweeted local resident Elke Bitzer.
- 'Tragic accident' -
"We are deeply saddened by this tragic accident and the death of an employee," said Chempark head Lars Friedrich.
Experts were racing to identify the composition of the smoke, he told journalists. Asked whether the cloud might contain toxic gases, Friedrich declined to speculate but said nothing could be ruled out.
City mayor Uwe Richrath said it was "a dark day for the people of Leverkusen".
Playgrounds in the city's Buerrig and Opladen neighbourhoods would be closed, he said. Residents were also advised not to eat fruit and vegetables from their garden.
By Tuesday evening, the city of Leverkusen said measurements of pollution levels taken throughout the day "were unremarkable", allowing the warning to shelter indoors to gradually be lifted.
People were however told not to touch or try to clean away any soot particles they might find on the street or on window sills, until further analysis by experts.
The last people to get the all-clear were those living closest to the blast zone in Leverkusen's Buerrig district.
- Large fire -
The explosion had sparked a fire in tanks used as storage for liquid solvents awaiting incineration, Friedrich said.
The blaze took several hours to put out, with firefighters from nearby Cologne called in to help.
Three of the tanks "were completely or partially destroyed", Friedrich said, making it impossible to tell for now where the explosion started.
Large numbers of police, firefighters and rescue crews were deployed to the scene, as well as pollution-detection experts.
Police in Cologne temporarily closed several motorways and told drivers to avoid the area.
Locals shared images on social media of the black cloud rising into the air, with some saying their windows were rattled by the force of the explosion.
According to a report in Der Spiegel magazine, the blast was measured as far as 40 kilometres (25 miles) away.
- 'Enough now' -
Leverkusen, on the eastern bank of the Rhine river, lies about 20 kilometres north of Cologne in the western state of North Rhine-Westphalia. It has a population of more than 160,000 people.
According to Currenta, the Chempark chemicals complex is one of the largest in Europe, with more than 70 companies based at its three sites.
The chemical incident comes as Germany is reeling from historic floods earlier this month that left at least 180 people dead in North Rhine-Westphalia and neighbouring Rhineland-Palatinate state.
Leverkusen too saw heavy flooding that damaged homes and cars.
"Corona, then the floods, now the explosion," wrote Twitter user Nico, from the nearby town of Leichlingen. "Enough now."