The beach is a breathtaking site, the Indian Ocean rolling endlessly toward dramatic hills of lush forest sloping down to the powdery sand.

But South Africa's Second Beach in the rural Eastern Cape is among the world's deadliest for shark attacks, with five fatalities in five years, three in 2009 alone.

"We're probably the most unsafe beach in the world at the moment," says Michael Gatcke, who from the verandah of his guesthouse witnessed a teenage surfer being mauled in January.

As for what is causing the sharks to attack, he muses, "It's easy to speculate but hard to pinpoint what it actually is."

Theories for the attack surge range from the shark-drawing blood of ceremonial animal sacrifices by traditional healers on the beach, to loud onshore music or a curse on surfers and lifesavers who have been the only victims.

Scientists say the attackers are mostly Zambezis -- the "pit bulls" of the ocean, also called bull or whaler sharks -- which are dangerously aggressive, grow to more than two metres (6.5 feet) long, and are known for shallow water attacks.

"I won't go out again. I've had it. From the first attack, I never liked water -- from the first one that I witnessed," said former lifeguard Gerald Mtakati, 36, who responded to each attack and has seen flesh savaged to the bone.

The renowned Durban-based KwaZulu-Natal Sharks Board is now investigating the attacks and plans to catch sharks and fit acoustic tags and receivers.

"I'd say it's pretty unusual, not in the number of attacks but the fact that they were all very, very aggressive attacks and resulted in fatalities in all cases," head of research Geremy Cliff told AFP.

"If you look at the national average it's probably one in six."

Zambezi sharks are at home in fresh water and likely drop their young in the giant Umzimvubu River estuary at First Beach, which lies east of Second Beach.

But what is puzzling both locals and scientists is the fact that the popular swimming spot was long considered safe from the apex predator.

"We've got no idea," said Cliff, who recently investigated two deadly attacks in the Seychelles.

"It's amazing the fact that that beach has been used for ages. Now, why all of a sudden have we had this spate of incidents? It's one of those things we can't just put our finger on."

South Africa accounted for two of six worldwide fatalities last year. There are shark nets in Durban and a sharks spotters programme in Cape Town.

In contrast, the Port St Johns municipality was briefly shut down last month by the local sheriff over money it owed to the lifesavers.

Authorities have long promised to look into the attacks, but the national government-funded study is only starting now and will look at understanding what is happening and not prevention.

Ndamase Mzimasi still volunteers as a junior lifeguard despite losing his brother in the deadly triple attacks in 2009.

"Sometimes it makes me nervous," the 19-year-old admitted, saying he's afraid to swim and sticks to the shallows.

Gatcke hasn't surfed at Second Beach since screams filtered up to his verandah as teenage surfer Zama Ndamase, whom he mentored, was being attacked.

"I haven't surfed since that day," he said.

"As the swell came past I just saw the red in the swell behind him and then that's when my heart just... that's when I knew ok, this is really an attack."

The 46-year-old closed his surf school in 2009 but had thought of the fatalities as a coincidence, as multiple attacks have been known to happen.

"But then after Zama's attack, it was very close to home and also sort of a realisation that there is something definitely going on here. It's not just the norm," he said, "and that's what scared me."