Fourteen passengers on Flight DL251 received medical assistance after the plane landed safely at Francisco Sa Carneiro Airport, a source at Portugal's National Emergency and Civil Protection Authority told Portuguese news agency Lusa. The four hospitalized were taken to Sao Joao Hospital in Porto with minor injuries from smoke inhalation.

The Airbus A330-300 was flying from Barcelona with 296 people on board, 12 of whom needed oxygen in flight.

Delta said the flight diverted because of a mechanical issue but gave no further details, Reuters reported. The civil protection authority told AFP the cause of the smoke was not immediately known.

Airport operator ANA Aeroportos de Portugal told the news site Observador that the jet diverted for technical reasons and that the flight to Boston was expected to depart on Sept. 28.

A Delta Airlines passenger jet. Photo by Reuters

The airport's emergency plan was activated, and Correio da Manha said 67 personnel from fire brigades across the Porto district were at the scene.

Flights at the airport were halted for a few minutes during the emergency.

The aircraft is about 11 years old and joined Delta's fleet in June 2015, according to fleet data from aviation news site The Aviation Hub.

Delta is the world's largest airline by revenue, having brought in a record $63.4 billion in 2025, according to Aviation Week. With its Delta Connection regional partners, it operates up to 5,500 flights a day to more than 300 destinations on six continents, according to its website.