PAKISTAN widened its manhunt for human traffickers on Monday after a tragedy off the Greek coast last week that left more than 500 feared drowned, including many Pakistanis, officials said.

With no definitive casualty numbers announced, families continued to fear for the fate of their loved ones as the nation observed a day of mourning on Monday, declared by Prime Minister Shahbaz Sharif's government.

The fishing trawler packed with refugees overturned and went down last Wednesday off south-west Greece in one of the deadliest-ever incidents in the Mediterranean Sea. 

The vessel was carrying as many as 750 people, including scores of Pakistanis, when it sank in international waters.

A search-and-rescue operation has since been underway.

Pakistan’s embassy in Athens has so far identified 12 Pakistani nationals rescued by the coastguard.

So far, Pakistani authorities have detained nearly two-dozen suspects, including two key suspected traffickers in Pakistan, and at least 12 people involved in sending young men to Libya for the onward journey to Europe.

Pakistan’s Interior Minister Rana Sanaullah Khan said the country’s Federal Investigation Agency has launched a crackdown against human smugglers, arresting key suspects in the cities of Lahore and Karachi.

“All the people involved in this tragedy will be brought to justice,” the minister pledged.