A Vietnam Airlines A321 made an emergency landing at Hanoi's Noi Bai Airport yesterday due to what aviation officials called "technical problems", leaving hundreds of passengers frightened by the sudden drop of oxygen masks and the implementation of emergency procedures by cabin crew.

The scheduled flight, on December 16 late afternoon, was from HCM City to the north-central city of Vinh, carrying 135 passengers.

Vietnam Airlines denied rumours the aircraft had been hijacked by a passenger who was said to have broken into the cockpit.

Lai Xuan Thanh, head of Vietnam Civil Aviation Authority said that the aircraft was forced to make an emergency landing at Hanoi because of technical problems.

"Pressure in the cabin suddenly dropped," Thanh said. "Oxygen masks dropped and emergency alarms went off in the cockpit. The pilot requested emergency clearance to land at Noi Bai Airport."

Vietnam Airlines spokesman, Le Truong Giang, said, "Because of the pressure drop, the plane had to release oxygen masks and lowered its altitude from 35,000 feet to 13,000 feet."

After the plane landed at Noi Bai Airport, passengers were transferred to another flight so they could complete their journey to Vinh City. But 26 passengers were too shaken to continue their trip.

One passenger, Pham Thi Hoa, said, "When the plane shook, everyone was scared and thought that we were going to die. We just want to land safely."

Aviation authorities said the Airbus 321 involved in the incident had been in operation since 2008 and underwent a safety check was on November 12.