The spill occurred about 6:20 a.m. at Verallia North America/Saint-Gobain Containers.
Plant Manager Bill Mann said all employees have been accounted for, and there are no reported injuries.
He also said that additional information such as what caused the leak would have to come from company media relations officials.
Capt. Richard Long of the Dunkirk Fire Department said the leak can be sourced to the same tank that caused a similar problem at the plant in 2009, when more than 500 tons of molten glass leaked from holes in the bottom of the tank.
Friday morning, Long said, the molten glass was leaking from the sides of the tank.
"They've been nursing (the tank) since the last time it happened," Long said. "The tank has been due for a rebuild."
On Friday, the molten glass flowed into the plant's basement, but Long said a square retaining wall there prevented the leak from developing into more of a problem.
"That was a big help," Long said.
As many as nine area fire departments responded to Friday's spill.
The American Red Cross was on scene to provide relief to emergency officials and company employees, while an abundance of food and water was made available by fire officials and volunteers.
At 10:30 a.m.: A flurry of activity continued outside the Saint-Gobin Containers plant 4 hours after a leak was first reported to the fire department.
Multiple fire departments remain on the scene, and at least two ambulances are standing by. The American Red Cross is on the scene to provide relief to emergency workers and company employees.
There is an abundance of food and water to assist those working the incident.
There has been significant smoke at times, but that has mostly died down in the last hour or so. Other than smoke, there is nothing visible from the outside of the building to show what has happened.
EARLIER: As many as nine fire departments responded this morning to a molten glass leak at one of this community's largest employers. Saint-Gobain Containers reported a tank rupture at 6:15 a.m. today. A Dunkirk Fire Department official said this leak is a "bigger hole than last time." In May 2009, more than 500 tons of molten glass leaked. Plant manager Bill Mann said all employees have been accounted for, and there are no injuries. He also said that additional information such as what caused the leak would have to come from company media relations officials.