Pakistani Prime Minister Shehbaz Sharif is declaring a national day of mourning to commemorate citizens who died when a fishing trawler packed with migrants sank off the Greek coast.

As many as 750 men, women and children from Egypt, Syria, the Palestinian territories and Pakistan were on board the vessel, attempting to reach relatives in Europe.

The Greek coast guard has defended its response to the tragedy that has left more than 500 migrants presumed drowned.

The vessel sank Wednesday.

Sharif expressed his grief over the tragedy, saying that Monday would be observed as a day of mourning, with the national flag flying at half-staff.