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"
Our reporter Lewis Adams headed to West Mersea beach last night, when news of the incident emerged, and captured these images.
Full details of what happened are yet to be confirmed but we are expecting news from Essex Police shortly.
Image source, Lewis Adams/BBC
Image source, Lewis Adams/BBC
Image source, Lewis Adams/BBC
Image source, Lewis Adams/BBCA local councillor has described what happened as a "tragic incident" and says the area can be "very dangerous".
Carl Powling, Conservative councillor for Mersea and Pyefleet, told BBC Essex: "Without knowing exactly what's happened there, it's very difficult to speculate but people are very concerned.
"It's definitely a tragic incident and it does highlight the dangers of the tidal area we live in and the sea and what can happen."
Powling also says local residents were first on the scene before the emergency services and offered help to the services when they arrived.
Coastguard tape remains in place on the beach this morning.
However, there are no emergency services at the scene.
Image source, Tom Larsen-Wright/BBCA huge emergency service response got under way on the beach in Mersea, Essex on Wednesday evening.
Here's what we know so far:
Stay with us as we bring you more details.