The recordings are emotional and difficult to listen to, and we have chosen not to play them.
One caller said in a trembling, breathless voice that a gunman was shooting inside the building.
"I caught a glimpse of somebody. They're running down the hallway. Oh, they're still running and still shooting. Sandy Hook school, please," the woman said.
In the minutes that followed, staff members inside the school pleaded for help as Newtown police juggled the barrage of calls.
The 911 calls were posted on the town's website on Wednesday under a court order after a lengthy effort by the Associated Press to have them released for review.
A state attorney tried to block the release to shield the victims' families, but last week a judge ruled the calls would be made public.
In another call, custodian Rick Thorne says a window at the front of the school was shattered, and that he kept hearing gunfire. While on the line with Thorne, the dispatcher told somebody off the call: "Get everyone you can going down there."
"There's still shooting going on, please!" Thorne pleaded to Newtown's 911 dispatcher, as six or seven shots could be heard booming in the background. "Still, it's still going on!"
Twenty students and six adults were killed in the shooting rampage on the morning of Dec. 14. The gunman, 20-year-old Adam Lanza, shot his way into the school with a semi-automatic rifle. Lanza also killed his mother in their Newtown home before driving to the school, and he committed suicide as police arrived at the scene.
Seven recordings of landline calls from inside the school to Newtown police were posted. Calls that were routed to state police are the subject of a separate, pending freedom of information request by the AP.
The Associated Press contributed to this report.