A massive operation to round up thousands of escaped crocodiles intensified in flood-soaked South Africa on Friday, as the authorities attempted to reassure the public everything was under control.

"A large number" of 15,000 reptiles at the Rakwena Crocodile Farm in the far north of the country had escaped last Sunday amid torrential downpours, farm owner Johan Boshoff told AFP.

The staff were forced to open the gates to prevent a storm surge.

"We have no idea how many escaped. The dams are dirty. You can't see how many there are really," said Boshoff.

The animals have scattered far and wide making the recapture operation more tricky.

"A thousand have already been caught," said police spokesman Hangwani Mulaudzi.

"There was one that was also found in town yesterday evening," said Mulaudzi.

The croc was spotted next to a shopping mall in the town of Musina 120 kilometres (75 miles) away.

Disaster managers brought in to help the operation stressed there was little risk of crocodile attacks, especially with a small army working to round up the rogue reptiles.

"It's not something we should all worry about," said spokeswoman Dieketseng Diale.

"It's like Crocodile Dundee down here," she added, referring to the popular 1986 comedy about a crocodile hunter in Australia.

Efforts to capture the carnivores are taking place mostly at night, when their red eyes can be spotted with a light.

Farm spokesman Zane Langman told local television channel eNCA most were small and easy for his team to catch.

"The majority are 2.5 metres (8.2 feet) and less, so ... we just basically jump on their backs and tie them up, load them up and taking them back to enclosures," he said.

The bigger ones were trickier, he admitted.

"We tie straps around their mouths... then tie the legs behind the back, inject them with a solution that's basically a muscle-relaxant."

Television footage showed catchers wrestling with crocodiles in mud, then tying up the animals' limbs with ropes.

An expert confirmed the reptiles should not be too dangerous.

"On a crocodile farm, most crocs will be under three or four years of age, because that's the age when they are turned into handbags," said renowned Australian zoologist Adam Britton, known for his work with crocodiles on the Discovery Channel series Face Off.

"So most of these crocodiles are likely capable of giving a nasty bite, but not life-threatening."

But at least some of the crocodiles would escape capture, he added.

"Realistically, the chances of capturing them all are extremely slim," he told AFP.

"If they wanted to, these crocodiles could travel tens of kilometres in a day and would be long gone."

The environmental concerns with so many farm-raised crocodiles in the wild were unclear.

"I dont think youll see them munching their way through native terrestrial and aquatic wildlife populations," said Britton.

"In fact, its possible that the area wont be able to support that many crocodiles, because there would be too much competition for them all to survive," he added.

Heavy rains in northern parts of South Africa have provoked floods on notably the Limpopo River. The deluge wreaked havoc as far as neighbouring Mozambique, displacing tens of thousands of people on its way to the Indian Ocean.