Residents have complained about the chemical smell and a rumbling noise that can be heard from several miles away from the ExxonMobil Chemical Ltd facility at Mossmorran in Fife.
The Scottish Environment Protection Agency (Sepa) said air quality monitoring has shown no cause for concern and it will continue to monitor the situation.
ExxonMobil said it will need to continue flaring over the next few days as part of the process to bring the plant back to normal operations.
The latest incident comes after Sepa served ExxonMobil Chemical Ltd and Shell UK Limited with final warning letters last year following unplanned flaring at the Mossmorran complex in June 2017.
Terry A'Hearn, Sepa's chief executive, said: "On a weekend with beautiful weather here in Scotland the people of this community should be free to enjoy it so we're extremely disappointed that they've been inconvenienced by this incident.
"We're working with Exxon to make sure that the flaring is reduced as quickly as possible and we'll be measuring the impact to see what the effect has been.
"We'll also be looking at what has caused this incident and if any further action is needed the community can be assured that we will be taking it as your regulator."
Sepa said ExxonMobil Chemical Ltd has advised that flaring is likely to continue over the coming days.
Local people took to social media to complain about the latest incident.
One woman tweeted: "I'm extremely concerned about the flaring from #Mossmorran. The noise last night after 10pm was horrendous, it was like being behind an aeroplane with its back burners on".
Another wrote: "Will this be another night of #Mossmorran constantly rumbling on like a jet engine taking off? Chemical smell this morning too."
Stuart Neill, external affairs manager, for the ExxonMobil Fife Ethylene Plant said: "We absolutely understand the disruption that the current unplanned flaring is having on communities in the area.
"Our team are working round the clock to bring the plant back to normal operations, a process which will take a few days to safely complete. During this time we will, regrettably, need to continue to flare."
Neill continued: "The unplanned flaring was caused by a fault in a section of cable that resulted in the plant being moved to fail-safe mode as per established operational procedure.
"Flaring is an established industry practice, essentially producing water and CO2 from the combustion of Ethylene and steam.
"We are doing everything possible to minimise both the flaring and the timescales to resolve this unplanned event."
Fife's Green MSP Mark Ruskell said: "Once again, people's lives are being significantly disturbed by this aging chemical plant and a flare visible from all the way over in Edinburgh.
"What should have been a relaxing Easter weekend has become a distressing few days for the communities around the plant."
Lucinda Cameron is a journalist for Press Association Scotland.