Sharks have gathered off a coastal electricity plant in northern Israel where the Mediterranean waters are warmer, prompting authorities on Monday to warn people to keep away.

Dozens of sandbar and dusky sharks, which can reach up to three metres (10 feet) in length, are attracted to the Hadera plant that uses seawater to cool its turbines before discharging the warmer water back into the sea.

Images of the sharks have created a stir among Israeli divers seeking the ultimate thrill of swimming with the predators and taking pictures with them.

The Israeli Nature and Parks Authority and the Israel Diving Authority issued a warning to protect both the public and the sharks from close and potentially lethal encounters, noting that sharks are a protected species that cannot be fished, fed or harassed.

While the past decade has seen a steady growth in the number of sharks seeking warm spots off Israel's Mediterranean coast, experts are still unsure what draws them there.

"We know they like being in the warm waters, but we don't know exactly why," Nature and Parks Authority marine ecologist Ruth Yahel told AFP.

"You can see they're drawn to the warm water -- they enter its stream and perform a Rondo-like dance, fly out with the stream, circle around and do it again," she said.

"They might do it because it's fun, or pleasurable to be in the warm water."

Other possible explanations to the warmer water's appeal could be a relative abundance of prey, protection from parasites or a meeting point for mating.

But "these are all theories, we don't really know", Yahel said.

While shark populations in the Mediterranean are in decline, the number of sightings off Israel has been rising in recent years, according to Yahel.

"The impression is they're arriving here more," she said, with scientists unable to explain the phenomenon.

There have not been any recorded incidents of sharks attacking people off Israel's Mediterranean coast for decades.