The Pakistan International Airlines Airbus A320 crashed on Friday into a residential district of Karachi. Two people on board survived.
Flight PK8303 came down about a kilometre short of the runway as it was making a second attempt to land.
"The search resumed this morning and the voice recorder was found buried in the debris," spokesman Abdullah H Khan said in a statement.
"The cockpit voice recorder recovery will help a lot in the investigation."
The flight data recorder had already been found.
Officials and Airbus investigators are collecting evidence at the site as they try to determine the cause of the country's worst airline disaster in years.
Under international aviation rules, French investigators from the BEA - the French air safety investigation authority for civil aviation - have joined the Pakistan-led probe because the 15-year-old Airbus jet was designed in France.
The BEA said in a statement the two recorders would be examined at its laboratory just outside Paris. It issued a photograph of one of them on Twitter showing that it appeared to be intact inside its crash-resistant shell and metal base.
The plane's CFM56 engines are expected to be a focus of the investigation after the pilot reported both had failed shortly after the plane made an initial, unsuccessful attempt to land.
The engines were made by CFM International, a joint-venture of France's Safran and General Electric, and are among the most widely used and reliable in the airline industry.
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