Celebratory gunshots fired at a girl's 18th birthday party triggered more gunfire that left two people dead, two critically injured and nearly two-dozen injured in a chaotic scene where people jumped from second-floor windows to escape the shooting at a suburban Houston home, authorities said Sunday.

Harris County Sheriff Adrian Garcia said the gathering Saturday night was openly promoted using multiple social media sites, drew more than 100 people, most of them 17- to 19-year-olds, and became a "birthday party gone wild."

He said it appears partygoers were dancing in the home when someone armed with a pistol shot into the air in celebration. In the ensuing confusion, another person who was armed began firing into the crowd, Garcia said. Young people then streamed into the narrow street to avoid the burst of gunshots that followed shortly before 11 p.m. Saturday.

Partygoer Shaniqua Brown — who said she heard about the party through Instagram, a photo-sharing app and website — told The Associated Press it "was not rowdy at all." She said she first heard gunshots in the house and they continued outside as people fled and sought cover.

Authorities have given varying accounts of the number of people injured, but they clarified Sunday that 20 were hurt, with 16 suffering gunshot wounds and four others varying injuries such as a fracture and twisted ankles in the panic to flee.

The two people killed, one an 18-year-old male and the other a 16-year-old female, were students at Cypress Springs High School, Garcia said.

He chastised the party organizers, who advertised the event on social media, saying "you have no control on who to expect at your door."

Authorities are searching for two gunmen, he said, one who's about 17 years old and the other believed to be about 22.

"It's a horrible combination of immaturity, access to a firearm, and the inability to control one's self," he said.

Garcia said party organizers arranged to have people searched as they entered the home. "Anytime you have to factor in a bouncer and being searched at the door, you have already taken a turn for the worse," he said.

Sheriff's spokesman Thomas Gilliland said earlier that deputies were confronted with "mass chaos" when they responded to the call in the residential neighborhood about 25 miles northwest of Houston, adding that "kids were literally everywhere." He said witnesses reported partygoers jumping from the second floor in their scramble to flee.

Mariah Boulden said the gathering was her birthday party. Boulden, who lives at the residence, said her brother and others were patting down people as they entered the home. Two men refused to be searched and walked away, she said, then apparently hopped a neighbor's fence and entered through a back gate.

"They wasn't supposed to be here whoever they was," Boulden said.

She said her family is planning a candlelight vigil at the home for the victims of the shooting.

Pools of blood were visible outside the two-story brick home Sunday, and the garage door was bent after people had pushed it upward while trying to escape.

Bruno Figueroa, who lives a few houses down the street, told The Associated Press he heard five to 10 shots. He looked out his window and saw a crowd of at least 30 people running down his street.

"Kids were running everywhere," he said.

Figueroa said people suddenly began ducking into back yards and behind vehicles in driveways, apparently trying to hide from a car that was slowly coming down the street. Figueroa said that from his upstairs window he could hear the people who were hiding nearby.

"They were crying, yelling, 'My brother got shot,' 'Why did they do this?'" he said.

Figueroa said as soon as the slow-moving car rounded a corner and then sped away, the people who had been hiding gathered back in the street.