Ms Kulsoom's health deteriorated late on Thursday and she collapsed in the Intensive Care Unit. She has not regained consciousness since then, reports Geo News.
She has been kept on a ventilator, life-support machine and emergency medicine.
Ms Kulsoom's daughter Maryam Nawaz, who is soon going to contest the upcoming general assembly elections on July 25, tweeted to inform about her mother's condition.
"Ami had a sudden cardiac arrest this morning when we were on the flight and is in ICU and on the ventilator since," Maryam tweeted.
Ami had a sudden cardiac arrest this morning when we were on the flight & is in ICU & on the ventilator since. Earnest request for duas.- Maryam Nawaz Sharif (@MaryamNSharif) June 14, 2018
She also requested people to wish for her speedy recovery. Several prayers followed.
Geo News quoted sources as saying that Ms Kulsoom's health was being closely monitored.
Earlier on Thursday, Nawaz Sharif and his daughter left for London to visit Ms Kulsoom, who has been undergoing treatment for throat cancer.
In 2017, she underwent a surgery to remove diseased lymph nodes after she was diagnosed with throat cancer. Following that, she has became weaker due to multiple treatments and therapies.