The trawler, FB Amraful Islam Saad, sank in the Fairway Buoy area of the port amid high waves during the storm at 7:30 pm, he said.

Crews of a Marshall Island flag carrier cargo ship, Vega Stetind, spotted the trawler while it was sinking and immediately rescued the 21 fishermen, said Md Riaz, an official of the ship's local shipping agent Toggy Shipping.

"All the rescued fishermen are from the Monpura area in Bhola and they will be brought to Mongla port through a pilot boat from the ship," said captain Shahin.