A leading Pakistani lawyer and human rights activist, Asma Jahangir, has died in the eastern city of Lahore at age 66.

Local media reported Jahangir died in a hospital on Sunday after suffering cardiac arrest.

"She was always on the front line for progressive voices, even when democracy was under threat," said Sherry Rehman, an opposition senator in Pakistan's parliament and Jahangir's friend.

"As a close friend, we bickered on issues, but she introduced me to human rights when I was a young journalist," she told Al Jazeera. "We are all reeling from shock, the global human rights community is bereft - one of Pakistan's brightest faces is gone."

Known for her persistence on advocating for issues including women's rights and discrimination against minorities, Jahangir was the first woman to serve as president of the Supreme Court Bar Association of Pakistan.

'Speaking truth to power' a phrase, we often use. #AsmaJahangir lived,practiced till her last breath. Questioned mullahs, military, judges, politicians, all the powerful;defended downtrodden. Faced threats &

attacks. Was never afraid.What a hero. We have to contend with a void. pic.twitter.com/NFamtObL0s — Raza Ahmad Rumi (@Razarumi) February 11, 2018

Critical of Pakistan's military, intelligence and armed groups, she braved death threats, imprisonment and beatings as she pushed for human rights cases.

She helped bonded labourers get legislation passed through parliament and worked on blasphemy cases.

She was arrested in 2007 by the government of then military ruler Pervez Musharraf.

"Pakistan mourns for losing one of its bravest daughters who fought for human rights. She will be remembered throughout the journey towards stronger women rights in Pakistan," Shehbaz Sharif, Punjab chief minister, told Al Jazeera.

Jahangir's supporters and colleagues took to social media to offer their condolences.

She is survived by two daughters and a son. Her daughter Muneezay is a leading journalist.

"Pakistan has lost its fiercest leader," said Salman Sufi, director general Strategic Reforms Unit of the Punjab Government.

He told Al Jazeera Jahangir propelled the issues of women's rights "in the darkest days faced by our country".

"Her role in getting the Punjab Women Protection Authority was undeniably crucial," he continued, referring to an order protecting women from violence by establishing centres across Punjab province.