A mother and daughter who died at a beach in Essex are named by family as Shally Rahman, 41, and Samiha Rahman, 15
Police believe they were trying to help a seven-year-old boy who had got into difficulty
He remains in a serious condition - three other people were also taken to hospital after the incident on Wednesday
The coastguard was called at about 17:35 BST - one witness says she saw three people appearing to get CPR
"It was absolutely horrific," says the witness, who praises the emergency services for their rescue efforts
Another witness says a man swam out three times to try to save the group: "Two of the children he brought back were not in good condition"
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.
BBC reporter Tom Larsen-Wright has been at the scene this morning.
Speaking to BBC Essex's mid-morning presenter Ben Fryer, he said islanders had woken up trying to come to terms with what happened last night.
"You can definitely tell that something has been happening in Mersea Island."
He said emergency services had now left the scene and the beach was busy with families.
Zoie O'Brien
Image source, Jamie Niblock/BBCThe beach has started to get busier now with families and dog walkers arriving for the day. Many are aware of the tragic incident which took place last night.
Local people have begun laying floral tributes close the where the tragedy took place, praising the emergency services for their efforts.
Rita Coombs, 70, was tearful as she described the rescue operation.
She and neighbours from nearby flats rushed to the scene last night with blankets, hoping to help the emergency services and anyone who may have emerged from the water.
Her neighbour, she says, heard a man screaming and “couldn’t speak” about what he had witnessed when he returned from the beach.
Local resident Rita Coombs says the whole island feels “very quiet”
We've just heard from East of England Ambulance Service about its response to last night's incident.
It confirms two people died at the scene, one person was taken to hospital by air ambulance and another three were taken by land ambulance.
A spokesperson said: "Following reports of multiple people in distress in the water at Sea View Holiday Park, West Mersea, we dispatched multiple resources including our Hazardous Area Response Team, critical care paramedics and two air ambulances.
"Sadly, despite best efforts, two patients could not be resuscitated.
"One patient was transported by air to hospital, and a further three patients were transported by road to hospital."
Ahead of the summer and during the recent heatwaves, the RNLI has promoted a number of water safety tips.
If you're heading to the coast, it advises:
If you do get in trouble in the water, follow its Float to Live guidance:
West Mersea is a small coastal town on Mersea Island, about 10 miles (16km) south of Colchester in Essex.
About 7,000 people live in the town on the western side of the island.
The sand and shingle beach is one of its main attractions.
According to the town council, the island becomes completely cut off from the mainland during a full and new moon.
Here is an aerial view of the beach this morning:
Rita Coombs, who lives in West Mersea, says she saw emergency services treating a group of people on the beach.
She says three people appeared to be receiving CPR.
"It was absolutely horrific. I can't praise the emergency services [enough], it was beyond all belief, they worked so hard."
She says she tried to support the emergency services during the "nightmare that was unfolding".
"The feeling was we just wanted to go out and help. Our hearts were going out to these people fighting for their lives."
She said the whole island feels "very quiet" this morning.
"It's a very sad island at the moment.
"We're just sending our thoughts to the people that have passed and the people left behind. It's tragic, absolutely tragic."
Tom Larsen-Wright
Image source, Tom Larsen-Wright/BBCI'm at West Mersea beach, where there is a feeling of sadness and shock.
Residents have told me they've never known such a big emergency operation on the island.
Locals were also quick to praise the community response, and the efforts the emergency services made to help those involved.
A bunch of flowers has been left on the beach.
Essex Police has released an update to say two more people are in hospital, with "non life-threatening" injuries.
The force previously confirmed two people had died and a third was in hospital in a "serious condition".
We now know that five people were involved.
Det Ch Insp Pitcher is appealing for anyone who was at the beach, who has not yet spoken to officers, to get in touch.
He said: "We are grateful to the people who have already spoken to us and helped with our inquiries.
"We would ask anyone who was at the beach at the time, and who has not yet spoken with officers, to please get in touch, to help us understand what happened.”
He also appealed for anyone with footage to get in touch with police.
Det Chief Insp Al Pitcher, from Essex Police, says officers believe the three people involved all knew each other.
"Today, our thoughts remain with the family members who are coming to terms with their loss," he said.
Essex Police says a third person remains in hospital "in a serious condition" following the incident, which happened at about 17:35 BST on Wednesday.
The force said it was called to the beach after reports that several people had got into difficulty in the water near Seaview Avenue.
A teenage girl and a woman in her 40s died in the incident at West Mersea beach on Wednesday evening, Essex Police has confirmed.
BBC Weather reported that high tide at West Mersea was due to be at 18:47 BST yesterday.
It predicted a height of 4.4 metres (14.4ft).
This relates to the height of the tide, measured above a fixed reference level used for nautical charts, and is not to be confused with the height of waves or depth of water.
We're still waiting for further details of what happened, but the Coastguard referred to it as a "tragic incident".
A sole bunch of red roses has been left on the beach.
Coastguard tape remains in place but emergency services have left the scene after last night's response.
We are awaiting confirmation of the exact nature of the incident.
Image source, Tom Larsen-Wright/BBC
Image source, Lewis Adams/BBCLocal MP Sir Bernand Jenkin says he is "sad and very shocked" about the incident.
"We don't think of West Mersea beach as a dangerous beach.
"I mean, there are tidal currents but thousands of people use it as this time of year and generally feels like a very safe place.
"We don't have the details of what happened... clearly, something unusual occurred but we'll have to wait and see what it was."
He praised the emergency services and said he expects the community will come together to support each other.
We are expecting an update from Essex Police shortly.
Image source, Tom Larsen-Wright/BBCClaire Douglas, whose house backs on to the beach, says the community "will mourn this", after an incident described as tragic by emergency services.
She says the noise from two air ambulances flying directly overhead was the first sign of a major incident.
"It's just so devastating to hear that something has tragically gone wrong last night.
"You just immediately knew it was something very, very serious.
"You just get caught up in the sort of panic thinking there's nothing I can physically do, you're just standing watching.
"My neighbour is an RNLI volunteer he immediately got called out. I haven't seen him but he didn't get in until late.
"Nobody left until they'd done as much as they could.
"It genuinely is a strong community... we will mourn this."