Four people were taken to hospital with chemical burns today after a cloud of toxic gas escaped from a chemical plant.
The casualties also suffered toxic inhalation after titanium tetrachloride fumes escaped from the Cristal Global site near Grimsby on the River Humber, the coastguard said.
One of the people injured was transferred to a specialist burns unit at Pinderfield Hospital in Wakefield, West Yorks, Humber Coastguard added, and all shipping in the estuary was halted for several hours.
Watch manager Mike Puplett described the incident, which happened at around 12.30am, as "serious".
Cristal Global, based at Stallingborough on the River Humber's south bank, specialises in making titanium-based products.
The wind was blowing from a south-westerly direction towards the north east at the time of the escape, taking the cloud across rural land and out to sea, Humber Coastguard said.
A spokesman for Humberside Police said the incident was under control and no-one living in the surrounding area was at risk from the fumes.
He said: "A plume of gas has escaped following an accident at a factory.
"It is dissipating naturally in the air and there is no risk to any surrounding area."
At least ten fire crews attended the scene, with firefighters using a blanket of foam to contain the spillage.
The emergency services said up to 100 people could have been working at the plant overnight.
Humber Coastguard said: "Firefighters put a fairly substantial foam blanket over the outstanding toxic fumes and gas.
"The incident has been contained."
Humber Coastguard said the no-sail order in the estuary was lifted at around 5am.
But a ship with an estimated 12 people on board earlier sailed through the fumes while they floated over the Humber, causing the boat to stop at Immingham.
The crew was checked over by paramedics and do not appear to have been harmed, coastguards said.
Mr Puplett said: "This has been a serious incident, which has involved many agencies working together.
"The incident is still ongoing and there is still a danger from the toxic fumes in the locality.
"We are hoping that 'normal service' on the River Humber can be restored as soon as possible."
Officials from the Health and Safety Executive are expected to launch an investigation into what happened.
Phil Leake from Humberside Fire and Rescue said the escape occurred after an explosion in a chemical vessel at the factory.
He added that the gas cloud would have dissipated "quite quickly".
Mr Leake told the BBC: "The gas cloud has been moving across the Humber....in incidents like this we monitor the weather constantly.
"We have mobilised an officer on part of the north bank to take some air samples."
He said there was no danger to the public, but was still advising people living nearby to keep their windows and doors shut.
"Anyone who thinks they may be suffering from throat inhalation should contact NHS Direct," he added.
A spokesman for Cristal Global at the Stallingborough site said the company was still investigating what had happened, and was currently unable to provide any more information.