Scotland's environmental watchdog has launched a formal investigation into an unplanned flaring at a chemical plant.
The flaring is into its fifth day at the ExxonMobil Chemical Ltd facility at Mossmorran in Fife.
The Scottish Environment Protection Agency (Sepa) said it had received an "unprecedented" 600 complaints from members of the public reporting a chemical smell and rumbling noise.
ExxonMobil has blamed the flaring on a fault in a section of cable.
The company said such incidents were "very rare" and that there was "no cause for concern in relation to air pollution and associated health".
However, campaigners said local residents were "living in fear" about the impact of the plant.
The company was served with final warning letters last year over a serious flaring incident which took place in June 2017.
Then in June 2018, Sepa and the Health and Safety Executive said they would carry out an investigation into further incidents at the plant.
What is chemical flaring?
Chemical flaring is used to relieve pressure without simply pumping potentially dangerous chemicals into the environment.
It generally happens when a problem has arisen and gas which cannot be processed properly is burned.
Flaring can represent a large loss of otherwise valuable products and energy capacity.
The process is regarded by industry experts as an important safety mechanism and is permitted through certain conditions.
Sepa chief executive Terry A'Hearn said it was "working hard" to ensure that ExxonMobil halted the latest flaring as quickly as possible.
"We have also launched this investigation into the incident," he said.
"The unprecedented number of complaints we have received is a clear message and it's one that we have heard powerfully and clearly.
"I want to thank everyone who has taken the time to help us understand the impacts of this flaring and I encourage people to continue to report to us."
He added: "The Mossmorran complex is a major industrial facility, where this type of flaring is a legitimate safety mechanism.
"But it's been happening too often, and the current level and extent of the flaring from ExxonMobil Chemical Limited is unacceptable."
James Glen, from the Mossmorran Action Group, said the latest incident had been "unprecedented in its intensity and geographical reach".
"Residents as far away as Dunfermline and Kirkcaldy have reported being affected by vibrations, chemical smells and noise from the plant," he said.
"Many in communities closer to Mossmorran had their holiday ruined, the roar and light of the flaring preventing sleep and frightening children, while the black smoke and reeking air made people fearful to go outdoors."
He said the case for holding a full independent expert investigation into the impact of the Mossmorran complex was now "irresistible".
"The authorities are effectively in denial with the operators," he added.
"They pretend each emergency flaring is a one-off, but it is now a regular and worsening occurrence as the plant passes its shelf-life."
Plant manager Jacob McAlister said the Fife Ethylene Plant was committed to working constructively with Sepa, and was already carrying out its own investigation.
"As Sepa acknowledges, flaring is an important and permitted safety mechanism," he said.
"There is no cause for concern in relation to air pollution and associated heath - as confirmed by Sepa's own monitoring."
He said unplanned elevated flaring was "very rare" at the plant.
But he added: "When elevated flaring occurs, we absolutely understand its impact on communities. As such, we will continue to strive to minimise impact by reducing unplanned events and duration.
"Our team is working day and night to safely bring the plant back to normal operations."