Pakistani police have arrested a fellow officer after he was accused of beating up an elderly Hindu man for not fasting during Ramadan, an incident that sparked a social media outcry.

The elderly man was pictured bloodied after the attack which reportedly took place in Ghotki district of Sindh province on Saturday just before sunset. The images were widely shared over the weekend.

Activists and outraged Pakistanis using the hashtag #JusticeforGokalDas called for the officer who allegedly attacked him to be arrested.

"Religion doesn't mean forced fasting & terrorising the weak. Shame on those who did this," tweeted one Pakistani user.

"Deplorable! Non-muslims should be allowed to eat food anytime they want. Stop terrorising them," said another.

Bilawal Bhutto, son of Pakistan's slain prime minister Benazir, later tweeted that the police officer had been taken into custody.

Local police confirmed the arrest and told AFP an inquiry was being conducted.

"Strict action will be taken against the police official and a senior police officer will go to meet the victim and seek an apology to give a better image of the police to the public," a statement said.

Eating or drinking in daylight hours during Ramadan is a crime for Muslims in Pakistan. They can be fined or even jailed for up to three months.

The restrictions do not apply to other religions.

Ramadan is the most sacred month of the Islamic calendar and Muslims fast from sunrise to sunset every day during the whole month.