The Boeing 737-800 disappeared off the radar some five minutes after taking off at 2:37 am (0037 GMT) during a thunder storm and heavy rain, airport sources said. It was heading for Addis Ababa.
"(The crash) site has been identified three-and-a-half km (two miles) west of the (coastal) village of Na'ameh," Aridi told reporters at the airport.
He said search and rescue operations were under way but declined to give further details. He said it was too early to say what caused the crash but confirmed the plane took off in stormy weather.
An investigation into the cause was under way, Aridi added.
Eight-three passengers and seven crew were aboard, Aridi said. Fifty-four were Lebanese, 22 Ethiopian, two were British and there were also Canadian, Russian, French, Iraqi and Syrian nationals.
Witnesses said Lebanese army patrol boats were searching a small area off Na'ameh, which lies 10 km (six miles) south of Beirut. Aridi said the authorities had requested help from UN peacekeepers and some neighbouring countries.
A police spokeswoman in the nearby island of Cyprus said that a Cypriot police helicopter had headed to the crash scene to help the search for survivors.
A spokesman for the British military stationed in Cyprus said they were on standby to provide assistance and that there were two UN helicopters on the scene.
According to one source, residents on the coast saw a "ball of fire" crashing off Na'ameh.
Senior Lebanese officials and some family members of the passengers headed to Rafik Hariri International Airport after news of the crash. The plane had flown in from Addis Ababa earlier in the night, airport sources said.
State-owned Ethiopian Airlines, which could not immediately be reached for comment, has positioned itself as a major player in international air traffic in Africa and has recently expanded its Asian network.
It has regular flights to Lebanon, catering for business clients and the hundreds of Ethiopians who work there as domestic helpers.
Last Friday the airline announced an order for 10 of Boeing's Next-Generation 737-800s for a total price of $767 million. (China Daily)