A gang of poachers killed a rare one-horned rhino at a wildlife park in northeast India, taking to 15 the number of such beasts slaughtered this year, an official said on Sunday.

Heavily-armed poachers fired at the rhino late Saturday inside Assam state's Kaziranga National Park and its horn was gouged out, just a day after another giant pachyderm was killed, a wildlife official said.

"Two rhinos have been killed in two days and it is a matter of concern for all of us," a park ranger told AFP by telephone, requesting not to be named since the state government has gagged officials from speaking to the media.

"Poachers used AK-47 and 303 rifles to shoot dead the rhino. We have recovered empty cartridges from the site of the incident," the official said.

Kaziranga has fought a sustained battle against rhino poachers who kill the animals for their horns, which fetch huge prices in some Asian countries.

The main market for the horn is China where it is used for making medicine and jewellery while in Vietnam many believe the horn has cancer curing and aphrodisiac qualities.

At least 21 rhinos were killed last year by poachers in Kaziranga, about 200 kilometres (120 miles) from Assam's main city Guwahati.

A 2012 census in the park put the number of the rhinos at 2,290 out of a global one-horned rhinoceros population of 3,300.

The species fell to near extinction in the early 1990s and is currently listed as "vulnerable" by the International Union for Conservation of Nature, one notch away from "endangered".

The opposition parties have hit out against the state government for failing to combat rampant poaching.

"Poaching has been going on and the government is unable to check it. We see a definite nexus between forest officials and poachers," Sarbananda Sonowal, a local leader of the Bharatiya Janata Party, told AFP.