In one of the recordings released, a distressed caller is heard saying: "I think there’s somebody shooting in here at Sandy Hook School."
"What makes you think that?" she is asked.
"Because somebody's got a gun. I saw a glimpse of somebody, they're running down the hallway," she replies.
"They're still running, they're still shooting."
In an emergency call from Rick Thorne, whose job title at the time was Acting Head Custodian at Sandy Hook, gunshots are heard as he pleads "it's still going on!"
"I keep hearing shooting. I keep hearing popping," he tells the operator.
Thorne also describes how he thinks the gunman entered the building: "The front glass is all shot out. It kept going on," he says.
During the call the operator is heard asking a colleague to alert state police to the "active shooter".
Towards the end of the recording, loud bangs are heard in the background. This has been edited out of the clip above.
A court order has forced the publication of recordings of emergency calls made to police during the Sandy Hook school shootings in Connecticut, USA, last year.
Operators can be heard responding to witnesses including a teacher and a caretaker who report hearing gunshots.
Prosecutors had tried to block the release of the audio files but a legal challenge from the Associated Press news agency ensured the recordings were made public.
Former pupil Adam Lanza, 20, fatally shot 20 schoolchildren, six members of staff, his mother and himself on 14th December 2012.
Police in the United States made clear this evening that families of the 26 victims of the Sandy Hook school gunman will never know why he shot them.
The family of Victoria Soto, a teacher who shielded her students before being shot to death by Adam Lanza, said the release of the report into the massacre is "yet another blow that our family has been dealt."
"While others search for the answer as to why this happened, we search for the how. How can we live without Vicki? How do we celebrate Christmas without Vicki? Those are the questions we seek the answers for. There is nothing in the report that will answer those for us," the family statement said.
Yale University is no longer in lockdown after lifting its security alert for the entire campus.
The university had been on lockdown following an anonymous call to police in which someone claimed their room-mate was en route to the university's Old Campus "with the intention of shooting people".
Pictures from inside the Sandy Hook Elementary School released by Connecticut authorities show how Adam Lanza shot his way into the school building through a glass window.
He went on to kill 26 people, including 20 children.
Police believe a phone call reporting a man was en route to Yale University's campus "with the intention of shooting people" may have been a hoax.
Yale University in New Haven, Connecticut, was lockdown following the security alert, with Yale, New Haven and state police among the forces who descended on the Old Campus in the hunt for the gunman.
New Haven Police Chief Dean Esserman said the anonymous caller, who is not believed to be a student, was the one making the threat.
Esserman said the FBI is using voice recognition software to try and determine the identity of the caller, who will then be arrested and charged.
"We're going to find the person who made that call, we're going to put handcuffs on the person who made that call," Esserman added.
Adam Lanza kept violent video games and articles describing various mass-shootings in his bedroom, the report into the Sandy Hook massacre revealed.
Previously unseen images from inside the gunman's home show more guns and ammunition as well as edged weapons, knives, swords and spears. The photographs also show Lanza's bedroom windows taped over with black bin bags.
Adam Lanza had 253 live rounds on his body when police found him dead in the Sandy Hook Elementary School. He killed 26 people, including 20 children in the attack, firing 154 rounds.
He carried nearly 14 kilograms worth of guns and ammunition, a State Attorney report into the Sandy Hook shootings revealed.
All of firearms Lanza used in the attack were purchased legally by his mother, the report said.