A woman trying to protect her dog has been killed by an alligator which pulled her into a lagoon at a private US resort, authorities said.

Cassandra Cline, 45, of Hilton Head Island, South Carolina, was walking the dog along a residential area of Sea Pines Resort when she was attacked, officials said.

The 8ft alligator was later found and put down, Sam Chappalear of the South Carolina Department of Natural Resources told the Island Packet newspaper.

“It appears the alligator went after her dog and she tried to protect it,” Mr Chappalear said.

The dog was unharmed.

Captain Robert McCullough of the Department of Natural Resources said: “It’s common practice when we have an aggressive alligator like that, we put it down, but it will take some take some time to confirm it’s the right alligator.”

Alligator attacks on humans are extremely rare, Mr Lucas said.

Since 1976, there have only been about 20 attacks on people in the state, he said. Until 2016, none of the attacks had been fatal. In 2016, a 90-year-old woman wandered away from a Charleston care home and was found dead in a pond.

Police at the scene with Sea Pines security
Police at the scene with Sea Pines security (Drew Martin/Island Packet/AP)

Blake Smith, 34, was leaving his house when he saw police cars and fire engines in the neighbourhood.

“I waited for about 30 minutes, then I started hearing rumours about what happened down the road from here,” he told the newspaper. “It’s odd because this is the first time we’ve heard about an aggressive alligator around a human in the five years that we’ve been living here.”

Mr Smith said alligators had been spotted in yards or pools, but Sea Pines had quickly removed them.

“They do a good job. This is just a sad incident,” he said. “I have a young son, so it’s kind of concerning to see something like this could happen.”

Sea Pines said in a statement that it is working with authorities “to ensure necessary access to the site while the investigation is under way”.