The 33-year-old’s male friend also died as he tried desperately to save her after she got into difficulty.
Police said the 34-year-old man went to into the water when he realised his friend was in trouble.
Local surfers went to their aid after seeing they struggled to get back to the beach and tried to revive them on the sand.
The tragedy happened around 2.30pm local time yesterday at a beach in Zambujeira do Mar in Portugal’s stunning Alentejo region.
Today respected Portuguese daily Correio da Manha reported the unnamed woman who died was four months pregnant.
It also claimed two friends who were with the Brits on holiday in the area witnessed the drama as it unfolded.
She was face-down in the water and was being bashed against rocks
Today, a hostel owner said he tried to save the couple.
Joao Mendes, 36, was having lunch at his home when he heard the pair had disappeared in the water.
“I had been bodyboarding about 40 minutes before the tragedy and left to go home for lunch but I got a call telling me what had happened and I drove down to the beach with my board.
“I was the second or third bodyboarder to arrive. I paddled out and didn’t see anyone else at first. The waves were pretty big.
“I was heading further out to sea with another bodyboarder when we spotted the woman’s body.
“She was face-down in the water and was being bashed against rocks.
“We put her on my board and pushed her up onto the rocks and started practicing CPR.”
Jaao said another local then spotted the woman’s friend in the water.
They were in pretty bad shape and it was impossible. Neither ever had any pulse
He explained: “We put him on my board and brought him back to the same rocks.
“Other people including a nurse and a doctor had arrived by then and we split into two teams trying to revive them while we waited for the ambulance to arrive, but they were in pretty bad shape and it was impossible. Neither ever had any pulse.”
Police confirmed the dead pair were a British man aged 34 and a British woman aged 33 who were on holiday with a group of friends.
Maritime Police chief Rui Pedro Silva Filipe said: “I can confirm they are both British citizens. The man was 34 and the woman was 33.
“They were in Portugal on holiday with a group of friends.
“It appears the man went to the woman’s aid when he saw she was in difficulties and was holding onto a rock.
“He reached her but it was when they were coming back to the beach that they started drowning, maybe because they were tired.
“The local surfers went to their aid and got them out of the water to a small area of sand near the main beach but by that time they had already gone into cardiac arrest.
“Medical responders had already reached the scene and made an unsuccessful attempt to revive them by practising CPR.
“They were taken to a local health centre where they were pronounced dead and their bodies have now been taken to Beja where autopsies will take place probably tomorrow.”
A Portuguese Air Force helicopter took their bodies to a hospital morgue in the nearby city of Beja.
Neither has yet been named.
The British pair have been described in Portuguese press reports as a couple but police sources said they thought they were just friends.
The beach where the tragedy occurred has no lifeguard service after September 15.
Mr Silva Filipe described the sea at the time of the drama as “a little bit rough.”
Local media published footage of the Portuguese Air Force helicopter airlifting the bodies from the beach as other sunbathers looked on.
Zambujeira do Mar hosts an annual five-day music festival called the MEO Sudoeste.
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The likes of Madness have played at the festival, which takes place in August.
A Foreign and Commonwealth spokesman said:“Our staff are supporting the families of a British man and woman following their deaths in Zambujeira do Mar, Portugal and are in contact with the Portuguese authorities.”