Elephants and rhinos could be extinct within the next two decades, conservation campaigners are warning.

Wildlife campaigners say an estimated 35,000 elephants and 1,000 rhinos are killed each year as demand for ivory and rhino horn drives increasing poaching rates.

This demand means both species could potentially be wiped out within the next 20 years.

The warning comes ahead of marches across the world demanding greater protection for the two species.

The Global March for Elephants and Rhinos kicks off on Saturday, with hundreds of people are set to march through London wearing elephant and rhino masks.

The rally is calling for measures to tackle the problem, including a full worldwide ban on the trade of ivory and rhino horn.

Campaigners are also calling for ivory and rhino shops and carving factories to be closed down with immediate effect, implementation of tougher penalties for wildlife crime, and urgent strengthening of law enforcement in the countries where the animals are found and the products are being consumed.

In pictures: Wildlife Trust for orphaned animals in Kenya Show all 10 1 /10 In pictures: Wildlife Trust for orphaned animals in Kenya In pictures: Wildlife Trust for orphaned animals in Kenya Kenya An orphaned baby elephant walks near its keeper at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi In pictures: Wildlife Trust for orphaned animals in Kenya Kenya The Daphne Sheldrick Wildlife Trust for Orphans is operated by Daphne Sheldrick, wife of late famous naturalist David William Sheldrick In pictures: Wildlife Trust for orphaned animals in Kenya Kenya An orphaned baby elephant walks at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi In pictures: Wildlife Trust for orphaned animals in Kenya Kenya Orphaned baby elephants play at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi In pictures: Wildlife Trust for orphaned animals in Kenya Kenya The orphaned elephants raised by the Trust are returned back to join the undomesticated elephant population in Tsavo National Park, where David William Sheldrick was the founder Warden from 1948 to 1976 In pictures: Wildlife Trust for orphaned animals in Kenya Kenya Elephants stay at the orphanage until they mature, usually between eight to 10 years old In pictures: Wildlife Trust for orphaned animals in Kenya Kenya An orphaned baby elephant drinks milk from a bottle at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi In pictures: Wildlife Trust for orphaned animals in Kenya Kenya A keeper feeds an orphaned baby elephant milk from a bottle at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi In pictures: Wildlife Trust for orphaned animals in Kenya Kenya A 9-year-old blind black rhinoceros named Maxwell wanders inside its pen at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi In pictures: Wildlife Trust for orphaned animals in Kenya Kenya An orphaned baby elephant feeds on leaves at the Daphne Sheldrick Wildlife Trust for Orphans within the Nairobi National Park, near Kenya's capital Nairobi

Research in August suggested ivory poachers are killing elephants faster than they are being born.

Sir David Attenborough, Sir Richard Branson, Rory Bremner, Joanna Lumley, Stephen Fry, Ricky Gervais, Damon Albarn and Michaela Strachan are among the high-profile names who have given messages of support to the march.

Co-organiser of the London march, Maria Mossman of Action4Elephants, said: "We're just ordinary people who care about these extraordinary animals.