The gas main broke at around 4 p.m.
National Grid had to shut the gas off to 290 homes in Lawrence and 60 in the Meadowmere Park section of Woodmere while the main was fixed.
The repairs have been completed, but that was just the beginning of the hard work for the utility.
National Grid now has to go to each home to shut the meters off.
They can't restore gas until they know no free flowing gas will pour into the homes.
60 workers are out in the field.
Once the meters are shut off, they can turn the gas back on.
Then they'll need to go door to door again to turn the meters back on and relight the gas pilots.
A National Grid spokesman says gas will definitely be out through the night.
There's a chance it will continue into Tuesday afternoon depending on how long it takes the workers to get to everyone.