Leonard Casley, the self-declared lord of a chunk of the Outback, has died aged 93.

Prince Leonard was admitted to St John of God Hospital in Geraldton, Western Australia, on the weekend with a severe chest infection.

Family members confirmed the prince died in his sleep surrounded by family and friends early Wednesday morning.

Leonard Casley (pictured), the self-declared lord of a chunk of the Outback, has died aged 93

Prince Leonard was the ruler of Australia's oldest micro-nation, the Hutt River Province, founded in 1970

Prince Leonard was married to his wife, Shirley Joy Butler (left), also known as Princess Shirley, from Palmyra in Perth, for 66 years

Prince Leonard was the ruler of Australia's oldest micro-nation, the Hutt River Province, about 500 kilometres north of Perth.

He founded the province in response to a dispute with the State Government following an objection to wheat production quotas in 1970.

The micro-nation has its own flag and emblem but is not officially recognised by the government.

The self-described mathematician and physicist suffered from emphysema for 20 years.

The father-of-seven, who stepped down from the throne in 2017, has many grandchildren and great-grandchildren, Geraldton Guardian reported.

Prince Leonard was married to his wife, Shirley Joy Butler, also known as Princess Shirley, from Palmyra in Perth, for 66 years.

Princess Shirley died in July 2013.

Prince Leonard founded the province in response to a dispute with the State Government following an objection to wheat production quotas in 1970