Levies official Balach Gichki told Dawn that the speed boat was on its way from Gwadar district's Jewni area to the Iranian border when it sank, dawn.com reported.
He said four dead bodies were retrieved from the Arabian Sea, whereas a search operation initiated by the locals was under way to recover the remaining seven bodies.
"People were engaged on their own in rescue efforts", Gichki stated.
The dead bodies are yet to be identified.
"The boat was overloaded and all of a sudden it somehow sank", Gichki said quoting locals.
He said the victims were illegal immigrants from Pakistan trying to enter into neighbouring Iran illegally.
Thousands of Pakistanis trying to enter Iran illegally are caught every year by Iranian border guards. Iranian authorities had been often deporting Pakistanis entering into their country.
Unemployment and poverty-hit Pakistanis in search of jobs sneak into Iran via unfrequented routes, found within the 900 kilometres porous border.
Illegal immigrants from Pakistan travel through deserts of Iran and Turkey on their way to Greece. Very few manage to reach that country, whereas a majority either get caught in Iran or Turkey.