An Italian DC9 airliner with 81 people aboard disappeared today over the Mediterranean Sea on a domestic flight to Palermo and an airline official said the plane "must have crashed."

A spokesman for the domesic airline Itavia said the plane took off from Bologna in Northern Italy for Palermo, the capital of Sicily.

The plane had enough fuel for a three-hour flight. It carried 77 passengers, 13 of them children, and a crew of four. No information was available on the nationality of the passengers.

A small armada of Italian Navy ships, diverted ferry boats and tug boats, backed by helicopters and reconnaissance planes equipped with searchlights, searched a wide area of the sea 80 miles southwest of Naples where the plane disappeared from air control radar screens shortly after 8:55 a.m. (2:55 p.m. EDT).

At Palermo airport, weeping relatives of passengers and crew members waiting through the night. At midnight, an Itavia spokesman told reporters, "We have to consider the plane must have crashed."

Rome air traffic controllers said the last radio contact was about 50 minutes after takeoff when the pilot said he was near the island of Ponza, 70 miles west of Naples.

Italian officials said that strong winds and heavy seas were hampering the air-sea search for the plane.