Police were searching for the gunman or gunmen who opened fire at a Sweet 16 birthday party in Riviera Beach, Fla., killing two teens and injuring six others.

The shooting happened late Saturday night outside Newcomb Hall. More than 100 people had gathered inside the building for the birthday celebration, wptv.com reported. 

According to wpbf.com, witnesses said a fight broke out and then gunshots followed.

"It went off like five or six times like, crack, crack, crack, crack, crack," Steve Siciliano, who witnessed the shooting, told wptv.com.

The victims were all males between ages 16 and 32, Riviera Beach officials said.

One teen died at the scene and another was pronounced dead at a hospital.

Watch the most-viewed videos on NBCNews.com

At least six other people were shot, but none of their injuries was believed to be life-threatening, city spokeswoman Rose Anne Brown said, The Orlando Sentinel reported. 

"You need to just turn yourself in," Riviera Beach Mayor Thomas Masters said of the shooter, according to wptv.com. "Make my day. Joe Lewis says, 'You can run, but you can't hide.' Just turn yourself in."

More content from NBCNews.com:

• Russell Crowe gets lost kayaking off Long Island
• Flood threat from troubled canal lock near New Orleans eases
• Hundreds take part in 'March on Wall Street South' in Charlotte
• Deputy shoots, kills 'out-of-control' inmate at hospital
• Parents' Facebook sting helps catch sex offender
• Video: Recipes revealed for White House's homebrewed beers

Follow US News from NBCNews.com on Twitter and Facebook

The boy, from Sayreville, New Jersey, was on a double-decker bus with about 65 other teenagers headed to New Jersey for a sweet sixteen party, according to Port Authority spokesman Al Della Fave. 

They boarded the bus in Queens and crossed over the George Washington Bridge to New Jersey shortly after 6:30 p.m. ET on Friday.

As the bus exited the upper level to head toward Interstate 95, the boy opened the top hatch of the bus and stuck his head out, Della Fave said. His head struck the underside of the Fletcher Avenue overpass, causing extreme trauma.

Read the story on NBCNewYork.com

The boy was rushed to Hackensack University Medical Center, where he was pronounced dead, police said.

No other physical injuries were reported, but the other teens on board the bus appeared to suffer severe emotional trauma. They were taken to a bridge administration building on a lower lot, where their parents picked them up, NBC New York reported.

Della Fave said two adults on were on board the bus at the time: the driver and an assistant. The assistant's role was not immediately clear.

Designer Transportation, which operates the bus, expressed its "deepest heartfelt sympathy" for the boy's family.

Police are continuing to investigate.

The accident caused long delays Friday night as the express lanes of the I-95 southbound from the bridge were shut down while emergency responders rushed to the scene and police investigated.

NBC New York and The Associated Press contributed to this report.

More content from NBCNews.com:

• Feds end probe of 'America's toughest sheriff' Joe Arpaio, no charges
• Clint Eastwood's empty chair at RNC sparks Internet buzz
• Lawyer: Ex-Navy SEAL sought advice before publishing book about bin Laden raid
• Isaac outages add to La. heat; twister alerts inland
• For military members, early retirement is costly
• Video: Large parts of Gulf Coast submerged
• Obama orders VA to expand suicide prevention services

Follow US News from NBCNews.com on Twitter and Facebook