Armed robbers have raided one of Pakistan's leading charities and stole $400,000 in cash as well as five kilos of gold, police said Monday.

At least eight robbers struck at the Edhi Centre in the southern city of Karachi, taking several staff hostage and threatening the organisation's revered founder Abdul Sattar Edhi at gunpoint.

Edhi, aged in his 80s, is one of Pakistan's best-loved figures for his unstinting work providing ambulance services across the country and running shelters for women, children and the destitute.

Police said the robbers broke into the centre, where Edhi also lives, on Sunday and took the mostly female staff hostage.

Edhi, who has been on dialysis for the past year, was sleeping in his room and was woken at gunpoint by the robbers, who demanded the keys to the vaults.

The philanthropist told the robbers he did not have the keys which were held by his wife. The robbers then smashed the locks open.

"Our investigation is going on but it seems that some insider was involved in the robbery," Zahid Hussain, a police officer who is part of the investigation team, told AFP.

The robbers made off with five kilograms (11 pounds) of gold ornaments and about $400,000 in cash, he said. The value of the gold has not yet been established.

"The gold belonged to people who trust Edhi and gave it for safe keeping, while the dollars were kept to be paid by the charity on some account," Anwer Kazmi, Edhi's right-hand man, told AFP.

"It is a shameful act."

Edhi runs the largest network of ambulances in Pakistan and his charity organisation provide shelter and food to thousands of orphans and homeless women.

Always dressed in simple clothes of coarse black cloth, Edhi raises funds through donations from the affluent and through charitable drives during religious festivals.

Last year both of his kidneys failed and he undergoes dialysis twice a week.