(BSS/AFP) - Pakistan was searching Wednesday for a Boeing cargo plane missing off the coast of Karachi after radar showed it "rapidly descending," the Pakistan Airport Authority (PAA) said in a post on X.

The plane, operated by the private K2 Airways, had five crew members on board and was en route from Sharjah in the United Arab Emirates to Karachi when it went missing on Tuesday evening after reporting a "navigational system issue," the authority said.

At 21:21 pm Pakistan time, the aircraft was observed on radar "rapidly descending and with rapid heading change," and communication contact was lost about 155 nautical miles west of Karachi, the PAA said.

A rescue coordination center was activated and a search effort launched at sea to locate the missing aircraft, it added.

Preliminary data sent from the plane "indicated a loss of altitude, followed by a climb, and then a second, sudden and dramatic loss of altitude," according to Flightradar24.com, a global flight-tracking service.

K2 Airways is a private cargo airline in Pakistan that operates scheduled and charter flights domestically and internationally.

Manufactured in 1999, the plane flew as a passenger plane for Aeroflot and Garuda Indonesia before being converted to a cargo configuration in 2012, according to Airfleets.net.