A huge explosion at Tilbury Docks has caused the building's roof to collapse and a cloud of smoke to billow across the River Thames.
Residents near the site in Essex have described houses being shaken by the blast just before 10am on Friday.
Images posted to social media show the roof of the large industrial building partially caved inwards.
No injuries have been reported.
Shelia, 40, who lives nearby, told Essex Live she was was asleep when she woken by the noise of a “huge explosion”.
She said: “It was so loud it woke me up. After the huge explosion I heard loads of sirens and there was lots of police nearby.
“It’s dusty around here all the time so I didn’t notice that so much but I think it’s probably just because it’s too old. We have roadworks going on outside our house but it was so noisy I knew it couldn’t be that.
“There was a black helicopter overhead while it was all going on. But it’s happened inside the docks so we can’t really see what’s happening.”
One resident uploaded footage of the cloud on Twitter with the caption: "Hope everyone is okay, huge explosion made the house shake."
Another resident reported seeing a "mushroom looking cloud of smoke towards the river" and thought their "window was going to come in".
Aislinn Ladd, 42, who lives along the Thames in Grays, told the PA news agency she was "feeding the baby and suddenly it was huge noise, house shook, windows vibrated."
"I've never experienced anything like it, scared the hell out of me," she said.
A spokesperson from the Port of Tilbury said: "We confirm that there has been a major incident at the grain terminal within The Port of Tilbury.
"There have been no injuries reported and the emergency services are in attendance."
Essex Fire and Rescue Service said it was called to the incident at 9.55am.
