Two separate deadly diseases have swept through a pride of Asiatic lions in India, killing 23 of the endangered species in just three weeks.

There are only some 500 Asiatic lions, also known as Persian lions, left in the world and they are all restricted to the 1,400 square-kilometre Gir sanctuary in India's Gujarat state.

Authorities at the Gir park confirmed Tuesday that at least four of the lions have died from CDV (canine distemper virus) - the same infection that killed around 1000 lions at Tanzania's Serengeti National Park in 1994.

Asiatic Lions lounge in the shade of a tree near the village of Sasan on the edge of Gir National Park

The Gir sanctuary in Gujarat is home to India's entire population of Asiatic lions, believed to be just below 600

CDV attacks the gastrointestinal, respiratory and nervous system and leads to fevers and eye inflammation. It is almost always fatal.

At least 17 other lions succumbed to tick-borne babesiosis, a parasitic infection that affects red blood cells, causing weakness, lethargy and sometimes paralysis of the hind legs.

The Times of India reported that the 23 Asiatic lions who have so far died all belonged to the same 26-member pride. The last three lions are said to be 'battling for life', meaning the pride is likely to be entirely wiped out.

Asiatic Lion 'Ambar' in May 2016. Two separate deadly diseases have swept through a pride of Asiatic lions in India, killing 23 of the endangered species in just three weeks

The diagnoses of CDV, which can spread from wild dogs, have been confirmed by India's National Institute of Virology, said Gujarat environment minister Ganpat Vasava.

At the last official lion census in 2015, there were 521 Asiatic lions in the Gir sanctuary, but authorities said earlier this year that there were now more than 600.

However, the new deaths since September 21 will hamper the conservation efforts and mean the number may not have improved since the last census when the next count takes places in 2020.

The lions are also popular with tourists, who visit the sanctuary just to see the rare animals up close.

The CDV deaths have prompted authorities to run further tests on the 11 lions that died last month, according to D.T. Vasavada, Gujarat's chief conservator of forests.

'A team of experts is working to ascertain the reason for the viral infection. Since all 21 lions have died in one Sarasiya grassland, it is a matter of concern,' Vasavada added.

Local officials said another 31 lions from the same part of the sanctuary are being kept under medical observation, though they have not shown any signs of illness so far.

The Times of India said an action plan including vaccinating against CDV, implementing tick control measures and determining whether the virus came from wild hyenas or leopards was necessary to save the rest of Gir's lion population.

Video from the YouTube channel Contemporary Nomad shows a pair of male Adriatic lions close up to a safari vehicle

Janki, an Asiatic lioness, whose species is listed as endangered by the International Union for Conservation of Nature (IUCN), and are found as an isolated population in the Gir Forest of India's Gujarat state

Some conservationists suggest relocating some of the cats to another sanctuary.

Just 7 months ago, Gujarat's chief minister Vijay Rupani hailed the success of a major conservation campaign to save the Adriatic lion, which once roamed southwest Asia but was listed as 'critically endangered' in 2000 after a relentless onslaught of human poaching, hunting and encroachment on its habitat.

In the late 1960s, there were thought to be just 180 surviving Asiatic lions on the planet.

They are the cousins of the larger African lion and are believed to have split away around 100,000 years ago. Asiatic lions also have a distinctive fold of skin along their bellies.