Witnesses have described how the pilot of a plane that killed two people during an emergency landing was branded a "murderer" by horrified onlookers.
An 8-year-old girl and a 56-year-old man died when they were hit by the Cessna-152 plane on Sao Joao beach near Lisbon on Wednesday afternoon.
Dozens of sunbathers ran for their lives - some into the sea - as the plane landed and skidded across the sand, where parents were playing with their children, according to the Daily Mail.
Police confirmed the pair, an instructor and a pupil on a flying lesson, had been arrested and were being questioned.
Hundreds of people were on the beach at Caparica, 30km south of Lisbon.
One witness said the plane approached the beach in silence, so people only noticed it seconds before it came to land.
The 1978-built plane, which belonged to an air club, was being used for a flying lesson and the pilot reportedly told investigators he did not have time to land in the sea.
The nationalities of the victims is not yet known and according to local reports, they are not thought to be related. It was reported locally the parents of the girl were unharmed.
Witnesses said onlookers insulted the pilot in the moments after it became clear the little girl and the man, understood to be Portuguese and unrelated to each other, had been killed.
One witness known only as Mafalda, told a Portuguese paper how she was forced to grab her children and flee as the plane came down.
She said: "Those first moments were very tense. People wanted to attack the pilot and began to shout at him that he was a 'killer'. Everyone was really disgusted."
Lisbon Port police chief Paulo Isabel said: "Any loss of life is to be regretted but given the fact this plane came down on a beach with hundreds of people on it at the height of summer, we could have been looking at many deaths and many injuries."
A woman, 45, was treated for minor arm injuries.
The unnamed 56-year-old pilot was described by a spokesman at his flight school as "very experienced" with hundreds of hours of flight time.
Portuguese TV station SIC reported he had made a mayday call before signalling he had to land because of engine failure.
He was released after questioning along with his younger pupil pending an ongoing investigation, and the pair are due to be quizzed in court.
The plane belonged to an air club in Torres Vedras north of Lisbon but had been rented to a flight school called G-Air for several years.
The tragedy happened on a stretch of the beach near the Bicho d'Agua and Leblon restaurants. The beach, close to the mouth of the River Tagus, is more popular with locals than foreign tourists.
TV footage from the scene showed the plane by the waterline surrounded by firefighters as sunbathers looked on.
Journalist Enrique Pinto Coelho, who was playing on the beach with his son near where the plane came down, told Portuguese TV channel SIC: "I've just seen this plane make an emergency landing.
"It came down and advanced around 100m in the wet sand after it landed, taking two people who were lying on the beach with it.
"We were very near the landing spot and were playing football. It passed over the football pitch and we had to move back to avoid being hit.
"A large group of people surrounded the plane immediately. One of its wings was broken."
Police declined to comment on the cause of the crash, saying it was too early to speculate.
Maritime Police Chief Pedro Coelho Dias said the man and the girl were hit by the plane and died at the scene.
G-Air promised the authorities full cooperation and sent their condolences to the families of the victims.