Pakistan on Sunday released 220 Indian fishermen held for trespassing into its territorial waters as a "goodwill gesture" to its nuclear-armed rival India, officials said.

"We released 220 Indian fishermen today as a goodwill gesture," Deputy Superintendent of Karachi's Malir prison Hassan Sehto told AFP, adding that 219 others still remain in Pakistani custody.

The freed fishermen are expected to cross over into India on Monday.

Indian and Pakistani fishermen are frequently detained for illegal fishing since the Arabian Sea border is not clearly defined and many boats lack the technology to fix their precise location.

The fishermen often languish in jail, even after serving their terms, as poor diplomatic ties between the two neighbours mean fulfilling bureaucratic requirements can take a long time.

Relations between the two nations have plummeted since a deadly attack on an Indian army base in the disputed region of Kashmir in September, which New Delhi blamed on Pakistan-based Islamist group Jaish-e-Mohammed.

There have since been repeated outbreaks of cross-border firing, with both sides reporting deaths and injuries.

Kashmir has been divided between India and Pakistan since the end of British colonial rule in 1947. Both claim the Himalayan territory in full and have fought two wars over the mountainous region.