Gas supplies in the west of Ireland should be switched back on a phased basis over the weekend, energy chiefs have said.
Odourless natural gas which entered the network through Shell's Corrib gas refinery in Co Mayo is gradually being pumped back to the terminal at low pressure to be burnt off.
It may be Sunday before the 10,000 or so affected households and businesses will be advised it is safe to reconnect supplies.
Gas Networks Ireland, which oversees supplies, said it recommended users cut supplies using a valve on their meters because the gas could not be detected by smell in the unlikely event of a leak.
It issued an alert on Thursday evening to customers in Galway city, Oranmore, Tuam and Headford and Ballinrobe, Claremorris, Castlebar, Westport, Crossmolina and Ballina in Mayo.
Gas Networks Ireland have issued instructions on how to turn off your gas supply:
Ensure that all your gas appliances and pilot lights are turned off. Do not attempt to turn off the gas supply at the meter until your natural gas appliances are turned off.
Go to your meter. Locate the gas safety shut-off valve at your gas meter and turn it to the 'off' position. It is off when the lever is at a right angle to the pipe. If the gas safety shut-off valve is hard to reach or will not operate, contact Gas Networks Ireland on 1850 200 694.
In an update today it said supplies in Loughrea, Ballinalsoe and Gort were safe to be switched on.
"Restoring all customers is likely to take most of the weekend, on a phased basis. We are advising not to turn gas back on until told it is safe," Gas Networks Ireland said in a text to customers.
Natural gas is odourless, colourless and tasteless.
A chemical containing sulphur is added to it during the refining process for safety reasons.
It is believed one fifth of a day's supply entered the network from Shell's Bellanaboy terminal without the additive.
This is understood to have happened from Wednesday into Thursday before it was discovered by a worker in the refinery.
Shell E&P Ireland, which began refining and pumping gas from the Corrib field at the end of 2015, said it is the first time the issue has occurred in Mayo.
It said a "small quantity" of the odourless gas was in the system.
It is understood the supply would not have been pumped further south than Galway or east of Athenry in the county before the alarm was raised at about 3am on Thursday morning.
Subsequently, other gas supplies have been pumped into the network from the rest of the country to allow for the steady return of the odourless gas to Bellanaboy.
A spokesman Shell E&P Ireland insisted the refinery was operating safely.
"Work is ongoing to remove a quantity of un-odourised gas, which entered the Gas Networks Ireland (GNI) network," he said.
"Flaring is expected to continue today at the Bellanaboy Bridge Gas Terminal to remove the gas in a safe and controlled manner."
People living in the north Mayo area around the refinery are being updated with the flaring or burn-off of the odourless gas visible for about 20 miles and also audible over long distances.
The Bellanaboy terminal had been shut down for a number of days in the week before the technical issue with the odour additive occurred.
Shell said production was down to allow for routine maintenance at the refinery.
Gas Networks Ireland said it is working with priority customers such as hospitals to keep supplies on.
"We are working with the Corrib operator to resolve this issue and remove the un-odourised gas from the network in a safe and controlled fashion," the agency said.
"Our best estimate is that this may take between 48 and 72 hours."
Inspectors from the Environmental Protection Agency (EPA) are on site at the refinery while the flaring takes place.
The agency warned of increased noise levels and visual impact from the terminal.