Rescue teams with sniffer dogs have been deployed to sift through the debris, but parts of the site remain too dangerous to access.
Fourteen-year-old Adam Muller told the AFP news agency the explosion “felt like an earthquake”.
“I was asleep and suddenly there was this huge bang,” he said.
“I looked out of the window and just saw flames. It’s a massive shock,” he added.
National police commissioner in the Netherlands Janny Knol said there was “disbelief and uncertainty” in the community.
Dutch King Willem-Alexander and Queen Máxima said in a statement: “We sympathise with all those who have been personally affected or who fear for the fate of their loved ones.”
Police are expected to provide an update at 15:00 local time (14:00 GMT).
