LONDON (AFP) - Pakistan's Prime Minister Nawaz Sharif successfully underwent open heart surgery in London on Tuesday (May 31), his daughter said.

It was the 66-year-old premier's second major cardiac medical procedure in five years.

"Surgery successful by The Grace Of Almighty," his daughter Maryam Nawaz Sharif said on Twitter.

"All arteries successfully grafted," she told her nearly two million followers.

She posted a picture of Sharif lying in an intensive care unit bed with his eyes closed and said he was "stable".

The London hospital where the procedure was carried out was not officially named.

Sharif's surgery lasted around four hours, according to his daughter's tweets.

He is expected to stay in hospital for around a week to recover before travelling home.

A senior Pakistani government official told AFP at the weekend that Sharif, one of Pakistan's richest men, was paying all expenses from his own pocket and "none of the state expenditures are involved".

"It may take little over a week for the prime minister to recover and travel back to Pakistan," the official added.

A statement issued by his office in Islamabad on Saturday said he was being assisted by his secretaries and would be being kept abreast of day-to-day matters.

Sharif took power in a landslide in a May 2013 general election, for the third time since 1990.

Sharif has a power base rooted in Pakistan's richest and most populous province, where he is known as the Lion of the Punjab.

He has been under pressure since the so-called Panama Papers leak linked his family to a series of offshore companies.

The premier insists his family has done "nothing wrong", saying the claims had been investigated twice, decades ago, under the tenure of former military ruler Pervez Musharraf.

The leaked papers claim his children owned London property through an offshore company.

Sharif pledged to resign if the allegations concerning him and his family were proven.