Malaysian police probing the killing of the half-brother of North Korea's leader on Thursday arrested a second woman over the spy novel-style assassination Seoul said was carried out by Pyongyang agents.

A woman with an Indonesian passport was taken into custody overnight, a police statement said, and was being quizzed along with a 28-year-old Vietnamese woman detained on Wednesday.

The two women were arrested separately by detectives trying to get to the bottom of the murder of Kim Jong-Nam, the estranged playboy brother of Kim Jong-Un.

South Korean intelligence chiefs say he was poisoned by North Korean agents as he walked through Kuala Lumpur International Airport on his way to board a flight for Macau.

The portly 45-year-old had some kind of liquid sprayed in his face after being set upon by two women, Malaysian police have said.

He was rushed to hospital suffering from a seizure, but was dead before he got there.

CCTV images that emerged in Malaysian media, purportedly of one of the suspects, showed an Asian woman wearing a white top with the letters "LOL" emblazoned on the front.

Several more arrests were expected throughout the day, Deputy Inspector-General of Police Tan Sri Noor Rashid Ibrahim told national Malaysian news agency Bernama.

The first suspect, named as Doan Thi Huong, had been expected to appear in court on Thursday morning, but Selangor state police chief Abdul Samah Mat told AFP officers had obtained a seven-day remand order for her and for Indonesian passport holder Siti Aishah, aged 25.

- N. Korea 'objects to autopsy' -

Kim’s body was Thursday being held at Kuala Lumpur Hospital following an autopsy, the results of which have not yet been released.

North Korea had objected to the post-mortem examination being carried out, a senior Malaysian official familiar with the investigation told AFP.

"But we told them to follow Malaysia's laws," he added.

Malaysian media cited unnamed senior sources as saying North Korea had requested the body, but Abdul Samah said Wednesday that nobody had come forward and that it would remain in the morgue until it was claimed.

An official at the morgue said they had no indication who would claim the body or when.

But North Korean embassy officials were seen visiting the hospital's forensics department in a diplomatic vehicle on Wednesday afternoon and again overnight.

If confirmed, the assassination, which analysts said could have been ordered over reports Kim was readying to defect, would be the highest-profile death under the watch of the North's young leader Kim Jong-Un.

Jong-Nam was the eldest son of Kim Jong-Il, but on his father's death in 2011 the succession went to Jong-Un, who was born to the former leader's third wife.

The first-born had at one time been set to assume the leadership of his isolated country, but fell out of favour after an embarrassing attempt to get into Japan on a fake passport in 2001.

He has since lived in exile, with much of his time spent in the gambling enclave of Macau, where he was believed to have enjoyed some protection from Chinese security forces.

Known as an advocate of reform in the North and believed to have ties with Beijing's elite, Jong-Nam once told Japanese reporters that he opposed his country's dynastic system.

Reports of purges and executions have emerged from Jong-Un's North Korea in recent years, as the young leader tries to strengthen his grip on power in the face of international pressure over his country's nuclear and missile programmes.

In 2012 Jong-Nam sent a letter to his younger brother begging him to spare his life, a member of South Korea's parliamentary intelligence committee told reporters after news of the airport killing broke.