Romanian media has named the woman who plunged into the Thames to escape the Westminster terror attacks as 29-year-old architect Andreea Cristea.
Eyewitnesses told media they had seen a woman floating face-down in the Thames next to the bridge.
She has been identified by RomaniaTV as Ms Cristea, who was on holiday with her fiancé to celebrate his birthday.
It is not known whether she was thrown in by the impact of the crash or jumped into the water to avoid the carnage.
A spokesman for the Port of London Authority, which looks after safety on the River Thames, said: "A female member of the public was recovered from the water near Westminster Bridge. She is alive but undergoing urgent medical treatment on a nearby pier.
"We believe she fell from the bridge."
She was rescued alive but is believed to be in hospital.
Romanian media reports her fiancé sustained a broken leg and three broken fingers during the attack.
Ms Cristea and her fiance had reportedly just visited Westminster Abbey and the London Eye before they were injured in the attack.
Steve Voake (55) was walking across the Westminster Bridge towards the South Bank when he saw the aftermath. He said that he had seen a person in the water, as well as at least two bodies lying on the road and one in the water.
"I saw a trainer lying in the road and when I looked more closely I saw that there were a couple of bodies the other side of the road," he said.
"And when I looked over the side there was another body lying in the water with blood all around it."
London bus driver Michael Adamou, 25, was driving the 453 bus when he said he saw a grey Hyundai speeding in the direction of Parliament.
He said he believed at least one woman had jumped into the Thames to escape.
"The first thing I saw was the two people laying lifeless on the floor. They were on the pavement.
"He must have come down the whole side of the bridge on the pavement. I would say there were at least 15 or 20 people.
"When I was getting everybody off the bus, because they made us leave the bus on the bridge, I heard one guy come running behind me shouting his wife had jumped into the river to avoid getting knocked down," he said.
A spokesman for the Port of London Authority, which looks after safety on the River Thames, said on Wednesday: "A female member of the public was recovered from the water near Westminster Bridge. She is alive but undergoing urgent medical treatment on a nearby pier. We believe she fell from the bridge."
Additional reporting from PA
It was the terrorist attack that police and security services always feared, but hoped would never come. A man, dressed all in black, drove a car at 80kmh the full length of Westminster Bridge, aiming deliberately at pedestrians and cyclists.