A lion named Sylvester that escaped from a South African national park last year, roaming free for three weeks, has escaped again, a park official said on Tuesday.

Helicopters will be used to track down the three-year-old animal, which may be put down as a result of his repeated breakouts from Karoo National Park in the south of the country.

"He is clearly a troublesome lion and could be a danger to humans," South African National Parks spokesman Reynold Thakhuli told AFP.

"Authorities will have to consider various management methods to ensure his safety and that of people. Such interventions might include euthanizing the animal."

A signal from Sylvester's tracking collar, which was fitted after his last escape, showed he was outside the park on Sunday, and by Monday he was 20 kilometres from the park's fenced boundary, in a mountainous area not easily accessible by foot.

He has already killed a cow.

During his last escape, he roamed 300 kilometres from the park, killing 30 animals over three weeks before being shot by a tranquiliser dart fired from a helicopter.

At the time, wildlife officials said he had been forced out of the park by older lions.

"This time we don't know what might have driven him away. It could be that he became used to easy prey while outside the park," said Thakhuli.

Lions were re-introduced to Karoo National Park, in Western Cape province, in 2010 after an absence of almost 170 years.

The last wild lion in the area was shot in 1842.