“As a goodwell gesture, we released 172 Indian fishermen today,” Muhammad Hassan Sehto, superintendent of Malir district jail in Karachi, where the fishermen were held, told AFP.
The release coincided with a cricket blockbuster World Cup match between nuclear-armed arch-rivals Pakistan and India in Adelaide, Australia.
Sehto said 349 Indian inmates were still in custody, however.
Such arrests are frequently carried out by both countries as the maritime border in the Arabian Sea is poorly defined, and many fishing boats lack the technology needed to be certain of their precise location.
The fishermen often languish in jail even after serving their terms due to poor diplomatic ties between the arch-rivals.
Sehto said the freed fishermen will travel by train to the eastern city of Lahore, from where they will be handed over to Indian authorities at Wagah, the only active border crossing between the neighbours.
Another government official in Karachi confirmed the number and release of the fishermen. It was unclear how long they had been held prior to their release.
Last month, Pakistani marine forces arrested 38 Indian fishermen after they strayed into Pakistani waters.
Relations between Pakistan and India have taken a turn for the worse in recent months, with shelling on the disputed border in Kashmir.