Leonie Powling, an eyewitness, told the BBC: "We had people run to the cafe and say, 'We need help, we need help!'

"So we ran where they were running and then we could see that there were people in the water and people getting dragged out of the water.

"At the time, it wasn't 'What do I do?' It was 'You've been told someone is in danger,' so you're just running, you're just going there and helping the individuals who need it.

"We wished we helped a bit more, but we did what we could and now knowing that people have died, it's a lot sadder that we were there and kind of witnessed it."

Essex Police has just issued a statement.

Det Ch Insp Al Pitcher from Essex Police said: "My thoughts, and those of my team, are with the friends and family of the woman and girl who died yesterday.

“Since yesterday we have been working to establish the circumstances which led up to this incident. At this stage we believe they were trying to help a seven-year-old boy who had got into difficulties.

“The boy was taken to hospital where he remains in a critical condition but the woman and teenage girl, sadly, died.

“All the people involved in this incident are related to each other."

Police said they were speaking to "dozens of witnesses" as part of the investigation and urged anyone who might have more information to get in touch.

The family has now released a picture of Shally Rahman. 41, who died along with her daughter Samiha Rahman, 15 in West Mersea.

Paying tribute to his sister-in-law, Matiur Rahman said: "Shally was a helpful person.

"She was a housewife and looked after the kids. She was very good, actually."

Image source, Family handout

Matiur Rahman, brother-in-law of Shally Rahman told the BBC of the shock the extended family was feeling.

"We all feel very bad, my four brothers, my sister... everybody in the UK and back home. [In Bangladesh]

"My whole family - we are speechless. We can't believe what we heard from my brother.

"We are very shocked."

Paying tribute to his sister-in-law, he added: "Shally was a helpful person.

"She was a housewife and looked after the kids. She was very good actually."

Shally Rahman's brother in law, Matiur Rahman, was told in a phone call from his brother about the tragic events in West Mersea.

He was left in tears as he learned what had happened.

"They went in Colchester, [to the] seaside and they were near water and playing with them then suddenly a big wave came," he said.

He said about 10 members of family had been on the day out.

The family has released a picture of Samiha Rahman,15, who died along with her mother, Shally, 41, in West Mersea.

Image source, Family handout

Matthew Dilley teaches water sports and told the BBC: "Even the strongest swimmer would find it very, very challenging at the highest [point] of the tide going out."

He said where the incident happened is on an estuary - where, in this case, two rivers come in - which he said means "when the tide is coming out, it can be very strong".

Dilley added: "If you're unsure of the water, just wear a buoyancy aid or wear a floating device - to be safe at all times."

Image source, Jamie Niblock/BBC

BBC reporter Lewis Adams is at the scene this afternoon.

He said: "The police cordon has been removed and the beach is now fully open and plenty of families have returned to the sand and their beach huts.

"It’s a windy, but busy, scene.

"But the spectre of last night's tragedy remains - and there are lots of journalists here, all trying to make sense of what exactly unfolded.

"When I first arrived here you could see long spits and sandbanks in the water.

"Quickly, though, they have either been surrounded by water or totally disappeared beneath the surface.

"You can see how the area can soon become dangerous, particularly as the light fades."

Image source, Lewis Adams/BBC

A family friend from Colchester said the families involved had come down for the day from east London.

He said the father is a doctor of Bangladeshi heritage, but he “only knows the grandfather very well”.

“They are a very nice and likeable family" who were just "going for a day out”.

“We, as a whole community, are in shock actually,” he said.

A family member of Shally and Samiha Rahman has confirmed to the BBC that a seven-year-old boy remains in a serious condition in hospital.

A mother and her teenage daughter died after getting into difficulty in the water off the coast of West Mersea.

They have been named as Shally Rahman, 41, and daughter Samiha Rahman, 15.

Image source, Tom Larsen-Wright/BBC

Reverend Jo Parrott was about to give her children dinner when her husband, an RNLI volunteer, heard his beeper go off and headed out to the emergency.

"My husband had just got home from work. He's recently joined the RNLI team around here, so the first thing I knew was when his alarm went off and very shortly after that we heard helicopters and the sirens of the emergency services."

She opened St Peter and St Paul's church on Wednesday evening and again on Thursday for anyone affected by the incident.

She said the mood on the island today was "subdued and shocked".

"Our hearts are just breaking for those we now know were lost and for their family and friends," she said.

Beach hut owner Beverly Smit, 60, from West Mersea said a day-tripper from a neighbouring hut entered the water to try to help.

“He saw and they were calling for help and the children and adults were out there,” she said.

“He swam out, I think, three times. Two of the children he brought back were not in good condition.

“It’s not an easy swim when the tide’s coming in - you’re swimming against the tide, the water yesterday was particularly quite cold,” she said.

Smit heard the emergency response and by the time she got to the beach paramedics were attempting to resuscitate one person.

She and members of her rowing club have helped save people in the sea previously.

Image source, Lewis Adams/BBC

Bob Jenkins, Mayor of West Mersea told Radio 5 Live the coastal town was in shock.

He said: "We have thousands of visitors who come to Mersea each year and incidents like this are extremely rare, fortunately.

"Being an island, everybody pulls together, everybody looks after each other. They look after the visitors when they arrive, so this sort of incident is tragic and shocks everybody."

He said the water around the island is generally "extremely calm" but said "like all seas, they can be unpredictable and potentially dangerous".

He called the incident "very unusual and very tragic".

"The tide comes in quite fast, it goes out quite fast. There is always some element of risk and people need to be, and are, very careful, he said.

"This incident is extraordinarily rare and very saddening. I'm sure I speak on behalf of the whole community here - that we all pass our sincere condolences to the family and friends and we'll be thinking of them at this very difficult time."

Image source, PA Media

Prime Minister Andy Burnham has spoken about the tragic incident during a visit to Harlow in Essex.

He said the deaths were "very, very sad" and thanked "the emergency services who stepped in to help".

There are a growing number of tributes being left at the beach, including flowers and small trinkets.

Carl Powling, a Colchester city councillor, tells the BBC his 19-year-old daughter was working in a nearby cafe and went out with a few others to help.

"One of them was my daughter but all of the teenagers [were] absolutely remarkable."

Powling said one of them was on the phone to the emergency services while the others were stopping people from getting in the way and filming the incident.

He said they remained calm throughout it all.

Harriet Whiteside, 36, has brought flowers from her garden to show her respects to the people who died and the emergency services who helped.

"Everyone is really upset by what happened," she says.

Police officers have returned to the beach and are talking to people at the scene.

A woman was seen putting a yellow rose down at the beach as a way of paying her respects.