A mass shooting at a crowded bar in the southern US state of South Carolina has left four people dead and at least 20 injured, officials said.

Hundreds of people were gathered at the popular bar on St Helena Island in the early hours of Sunday morning when gunfire broke out, leading multiple victims and witnesses to run to nearby businesses for shelter, according to the Beaufort County Sheriff's office.

Four people were declared dead at the bar and at least 20 were injured, including four who were sent to local hospitals in critical condition, the sheriff's office said.

The incident is still under investigation, and the sheriff's office is looking into possible suspects, it said.

When police and first responders arrived, they found several people suffering from gunshot wounds, the sheriff's office said in a statement.

It's not clear if the shooting was random or targeted, and a spokesperson for the sheriff's office declined to share more details.

The bar where the shooting took place, Willie's Bar and Grill, offers Gullah-inspired cuisine and says on its website that it aims to spread the "heartwarming spirit of the Gullah Geechee culture". The Gullah Geechee people are descendants of Africans who were enslaved on plantations along the south-eastern US coast, including in South Carolina.

"COMPLETELY HEARTBROKEN to learn about the devastating shooting in Beaufort County," South Carolina Republican Representative Nancy Mace wrote on X.

"Our prayers are with the victims, their families, and everyone impacted by this horrific act of violence."

Willie's did not immediately respond to a request for comment from the BBC.