An ailing elephant at a Pakistan zoo died on Saturday, vets said, calling on the ill-equipped menagerie to evacuate her "mourning" partner to avert a second tragedy.

Pakistan's zoos are frequently accused of being blase about animal welfare, and the plight of Noor Jehan was cited by animal rights activists campaigning to shut the wildlife exhibition in southern Karachi city.

This month the 17-year-old African elephant underwent emergency treatment for a tumour which had crippled her back legs, but while in recovery she became trapped in her enclosure's pool.

Zoo workers hauled out the 3.5-ton pachyderm but she was unable to stand and lay stricken for nine days, "a life-threatening situation for elephants", said animal charity Four Paws International.

Experts were considering euthanasia but before a decision was taken "she succumbed to her critical condition", said a statement from the charity, which organised last-ditch medical efforts to save her.

Karachi Zoo director Kanwar Ayub confirmed Noor Jehan's death on Saturday and an AFP reporter saw her caretaker openly weeping outside her enclosure.

"It's very sad," said Four Paws International's Austria-based chief vet Amir Khalil. "Noor Jehan deserved a chance."

But the deceased elephant's pen pal Madhubala "should not have the same future", he told AFP, saying he plans to arrive in Pakistan on Sunday to assess her health and organise her evacuation.

"Karachi Zoo does not fulfil international standards and is not equipped to take appropriate care of elephants," the Four Paws International statement said, expressing support for a forced closure.

"It is now more urgent than ever that the remaining elephant, who is mourning her long-time companion, is transferred to a more species-appropriate location as soon as possible, to prevent another potential tragedy."

In April 2020, a court ordered the only zoo in Pakistan's capital Islamabad to shut after poor facilities and mistreatment of the animals there were revealed.

The facility had drawn international condemnation for its treatment of an Asian elephant named Kaavan, who was later airlifted to retirement in Cambodia in a project spearheaded by US popstar and actor Cher, and carried out by Four Paws.