A patron hiding inside the Pulse gay nightclub as a gunman carried out the worst mass shooting in modern U.S. history whispered to a dispatcher on a 911 call, "He is going to kill us."

The 911 call was among more than 20 released Wednesday by the Orange County Sheriff's Office. The sheriff's office assisted the Orlando Police Department in responding to the June 12 massacre that killed 49 people, including answering 911 calls when the police department's dispatchers were overwhelmed. Several of the 911 calls were from patrons trapped inside.

The Orlando Police Department has released only a fraction of the more than 600 emergency calls it received during the June 12 club shooting. A lawyer for the city of Orlando said this week in a court hearing involving a legal fight over the release of the records that more calls will be made public soon.

The man on the 911 call whispers that he is uninjured and hiding in a back room at the club, a little more than five minutes after the shooting started. The dispatcher at first seems confused, not realizing the man is talking about the nightclub shooting. But when she catches on, she tells him to stay where he is and that law enforcement officers have arrived.

It would be another three hours before SWAT team members breached a club wall to free patrons trapped inside and killed gunman Omar Mateen during a shootout. In addition to the 49 killed, another 53 were hospitalized. In explaining their response, Orlando police officials have said that the active shooter situation changed to a hostage situation after Mateen made it into one of the bathrooms where club-goers were hiding.

Some callers grew frustrated with the length of time it was taking to rescue people still trapped inside. A man whose girlfriend was communicating with him from inside a bathroom more than two and a half hours after the shooting started told a dispatcher, "This is the seventh time I'm calling. My girlfriend is at Club Pulse, sitting in a bathroom. Four dead, two wounded and they're about to die. Nothing is being done," he said. "If she calls me again, I'm a former Marine. I'm going to load up and head over there because obviously the police of Orlando can't do nothing."

The dispatcher urged him not to do that before he hung up.

In many of the calls, the callers — either patrons trapped inside or family members with loved ones at the club — try to hang on the phone as dispatchers, while sympathetic, tell them officers are at the scene and that they need to take other incoming calls.

A woman tells a dispatcher that her husband has called her from the second-floor of the nightclub where he is trapped. In another call, a sister says her brother is trapped in a bathroom. "He said there is a lot of dead people," she said.

"We are in the club, searching for everybody. We are pulling victims out," the dispatcher said. "Please just have patience."