University students have answered a hospital’s desperate plea for blood donations in southwestern Pakistan where 128 people were killed and hundreds injured by a suicide bomber during an election rally.

Friday’s attack in the province of Baluchistan was the deadliest in Pakistan in more than three years and took place just before ousted prime minister Nawaz Sharif was arrested as he returned to the country.

A candidate was among those killed in the election-related violence in the town of Mastung on Friday, while four others died in a separate strike in the northern town of Bannu.

The main hospital in the provincial capital of Quetta appealed for blood donations after being overwhelmed by bodies and casualties.

Dr Mohammad Waseem, who works at the hospital, said there was an overwhelming response to the appeal, mostly from university students.

Student Ali Ahmed, 18, said he turned up to donate blood in response to an appeal he read in a newspaper.

“That was a big tragedy in Mastung, I am very sad,” he told Associated Press. “If I can save a life with my blood, I am here to bleed for them.”

An injured man is carried to a hospital in Quetta, Pakistan, on Saturday, July 14, 2018, after a suicide bombing in Mastung on Friday. (AP/Arshad Butt)

On Saturday, banners condemning the tragedy fluttered over empty streets in Quetta, while lawyers seen wearing black armbands cancelled court appearances as the city mourned its dead.

“Stop killing people, stop shedding blood” read one banner, while another declared: “Terrorism and terrorist should be curbed with iron hands.”

Within hours of the attack, disgraced former prime minister Sharif returned from London with his daughter Maryam to face a 10-year prison sentence on corruption charges, anti-corruption officials said. His daughter faces seven years in jail.

A spokesman for Sharif's Pakistan Muslim League said the ex-prime minister and his daughter were being held in Adiala Jail, located outside the capital of Islamabad, on Saturday.

Sharif, who has been calling for supporters to vote for candidates from his party, is expected to appeal his conviction and apply for bail before the deadline expires on Monday.

He still faces two additional corruption trials, both of which will be held inside the jail.