A Boeing 737 plane with five crew has vanished after reporting a navigational system problem and losing contact with air traffic control on a flight to Pakistan.

Early data indicated the 27-year-old converted freighter operated by K2 Airways had possibly crashed into the sea south-west of Karachi after a series of sharp altitude changes before a steep final descent, according to flight-tracking service Flightradar24.

The cargo flight was on its way to Karachi from Sharjah in the United Arab Emirates.

The Pakistan Airports Authority said a co-ordinated search and rescue operation had been launched at sea through various agencies to find the missing plane.

Pakistan’s Rescue Coordination Centre is leading the search at sea.

The Pakistan Navy has divered a frigate toward the plane’s last known area, while Pakistan Air Force assets, and a Pakistan National Shipping Corporation vessel have also joined the search.

No wreckage or survivors have yet been found.

The ‌authority said the Boeing reported a ‌navigational system issue ⁠at 9.18pm on Tuesday (2.18am Wednesday AEST) while flying toward Karachi.

It said local air traffic control tried to guide the aircraft, but three minutes later radar systems showed the plane descending rapidly and communication was lost. The flight was about 155 nautical miles (290 kilometres) west of Karachi at the time.

Local media Geo ⁠News reported the plane had vanished while flying over the Arabian Sea near Ormara in Balochistan, Pakistan,

Flightradar24 said data showed the aircraft first lost altitude, then briefly ‌climbed, before ​a second, sudden and dramatic drop.

It added that the last transmitted data point placed the aircraft at 1100 feet ​(335 metres) above sea level, ‌with a vertical rate of -22,400 feet (more than 6800 metres) a minute, an extremely steep and abnormal rate of descent.

The missing ​aircraft is part of Boeing’s decades-old 737 family but is two generations older than the 737 MAX version that was involved in a recent safety crisis. It uses engines made by CFM International, jointly owned by ​GE ​Aerospace and France’s Safran.

The 737-400 was first delivered as ​a passenger plane to Russia’s Aeroflot in 1999. It was ‌converted to a freighter in 2012, according to Flightradar24.

It is K2 Airways’ only aircraft, after entering service with the carrier in 2024.

K2 Airways and Boeing did not immediately respond to requests for comment.

If casualties are confirmed, it would be the first fatal crash in Pakistan since 2020, when a Pakistan International Airlines Airbus A320 came down short of the runway ​in Karachi. It killed 97 people after pilots were distracted discussing the coronavirus before a failed landing attempt.

-with AAP