The warning was given after South Africa and Vietnam failed last week to sign a memorandum of understanding that would have led to them sharing information about rhino poaching.

Environmental Affairs Department spokesman Albi Modise said: "We had planned to sign the agreement at COP11 in India last week, but the Vietnamese minister was not available to attend the event."

He said the agreement would be signed before the end of the year.

More rhinos, 455, have been killed in South Africa this year so far than ever before. Last year the toll was 448.

"Since the spike in 2008, poaching has increased every November and December," said the Endangered Wildlife Trust's Kirsty Brebner.

Rehabilitation wildlife expert Karen Trendler agreed, saying: "Poaching is known to increase around Christmas."

But the number of rhinos killed might not reflect the true extent of the problem because poaching is under-reported, she said.

"Private game farmers are reluctant to report poaching because they don't want to alert other criminals to the fact that they keep rhino on their farm," Trendler said.

"Even the locations of the dogs that work in poaching prevention are being kept secret.

Trendler runs a rhino orphanage in Limpopo to help rehabilitate baby rhino that are left without a mother due to poaching.

“I am looking after three rhino orphans at the moment. There are a whole lot more coming, but I am not going to say where they are coming from due to security fears.”

Trendler, calling herself the “eternal optimist”, said there were efforts that were working to deter poachers although most were kept secret.

The technique of injecting a poisonous substance into rhino’s horn is taking off with just under 100 rhino now treated with the poison said rehabilitation expert Dr Lorinda Hern.

Veterinarian Dr Charles van Niekerk and Hern pioneered the technique of sedating the rhino and then injecting the horn with a poison in 2010. The poison does not affect rhino or birds such as ox-peckers but can be toxic to humans, so a dye is also injected into the horn as a warning.

While the rhino is under anaesthetic, a micro chip is inserted into the horn to help with tracking efforts should the rhino be poached.

This technique has been accepted by an insurance broker and insurance company who teamed up with Hern to offer insurance to owners of rhino.