The estranged half-brother of North Korean leader Kim Jong-un has been allegedly killed at the Kuala Lumpur International Airport (KLIA), according to the police.

Selangor Police chief Abdul Samah Mat said that a woman had reportedly approached Kim Jong-nam at the KLIA departure lounge and covered the victim's head with a cloth which contained an unidentified liquid.

"Jong-nam's eyes were stinging after the incident. He received help at the KLIA counter before being sent to the Putrajaya hospital.

"He was pronounced dead en route," said Abdul Samah, according to Berita Harian.

Meanwhile, Bukit Aman Criminal Investigation Department director Mohmad Salleh reportedly confirmed the death of the 46-year old Kim.

"At present, there is no indication that Kim Jong-Nam was murdered.

"The police has classified the case as sudden death for now," he was quoted as saying by Oriental Daily.

Bernama reported that the North Korean embassy has been informed of the matter.

The incident took place at 8am yesterday. Jong-nam was scheduled to board a flight to Macau. He arrived in Malaysia on Feb 6.

Jong-nam, the older half-brother of the North Korean leader, was known to spend a significant amount of time outside the country and had spoken out publicly against his family's dynastic control of the isolated state.

According to Reuters, South Korea's TV Chosun, a cable television network, said that Kim was poisoned at the KLIA by two women believed to be North Korean operatives, who were at large, citing multiple South Korean government sources.

The South Korean government source who spoke to Reuters did not immediately provide further details.

South Korea's foreign ministry said it could not confirm the reports, and the country's intelligence agency could not immediately be reached for comment.

Kim Jong-nam and Kim Jong-un are both sons of former leader Kim Jong-il, who died in late 2011, but they had different mothers.

Kim Jong-nam was believed to be close to his uncle, Jang Song-thaek, who was North Korea's second most powerful man before being executed on Kim Jong-un's orders in 2013.

In 2001, Kim Jong-nam was caught at an airport in Japan traveling on a fake passport, saying he had wanted to visit Tokyo Disneyland.

He was known to travel to Hong Kong, Macau and mainland China. He said several times over the years that he had no interest in leading his country.

"Personally I am against third-generation succession," he told Japan's Asahi TV in 2010, before his younger brother had succeeded their father.

"I hope my younger brother will do his best for the sake of North Koreans' prosperous lives."