The deaths of two children and two adults when a migrant boat sank off the coast of northern France should serve as a "wake-up call" to those in power, charity bosses said.
Fifteen others were taken to hospital but French authorities believe at least one more could be lost at sea.
One man drowned while the two children, aged five and eight, and the woman suffered cardiac arrests and never recovered after the sinking near Dunkirk yesterday.
French emergency services have said there is no chance of finding more survivors.
The search was called off on Tuesday night because of darkness and bad weather and did not begin again on Wednesday, an official with the French maritime agency for the Channel and North Sea region said.
It is believed to be the single biggest loss of life during the current migrant crisis, and brings the total number of deaths since 2018 to 10.
Clare Moseley, who founded the refugee crisis charity Care4Calais, called for the incident to be a "wake-up call" for those in power in the UK and France.
She said: "We are grieving for the victims, we stand in sympathy and solidarity with their families and friends.
"It is cruel and horrifying that, this time, young children are among the victims.
She added: "We have to provide a safe and legal process by which refugees can have their UK asylum claims heard, that's the way to put an end to terrifying, dangerous sea crossings and stop tragedy striking again."
Her views were echoed by the charity Save the Children, which said in a statement: "The English Channel must not become a graveyard for children."
Prime Minister Boris Johnson said the UK had offered "every support" to French authorities as they investigate the "terrible incident".
Home Secretary Priti Patel said she was "truly saddened" to learn of the "tragic loss of life".
Environment Secretary George Eustice doubled down on the government’s tough rhetoric this morning, blaming “callous gangs” for luring them across the dangerous Channel.
More than 7,400 migrants have reached the UK in small boats this year, up from 1,825 in 2019.
Mr Eustice told BBC Breakfast: “There is no reason for them to make this crossing, they are in safe countries, they are in the EU, they are in France.
“There isn’t a rationale, they’re not in danger and there is no reason for them to make a particular crossing. They are being encouraged to do so by gangs that are taking their money.”
Labour MP Yvette Cooper, chair of the Home Affairs Committee, said there had been fears “we would see a tragedy like this for a long time”.
She told BBC Radio 4's Today: “I don't think they [the Home Office] do have a clear enough analysis of the reasons why people are making this journey.”
Meanwhile, Lib Dem leader Sir Ed Davey described the incident “absolutely heartbreaking” and added: “The government has failed time and time again to provide a safe route for people with genuine reasons for wanting to seek asylum in the United Kingdom.”
Military resources and civilian boats were involved in the rescue operation after the vessel was seen in difficulty near Dunkirk.
The people on board are thought to have been trying to cross to the UK, despite wind gusts of up to 18mph.
The alarm was raised by a yacht which notified search and rescue.
French patrol boats and a helicopter from the Belgian air force were dispatched as well as a fishing boat.
Fifteen people were taken to hospitals in Calais and Dunkirk, according to the Maritime Prefecture of the Channel and the North Sea.
Searches were paused at 5pm due to lack of light and French authorities stress any assessment on numbers is provisional.
An investigation into the causes of the sinking has been launched by the Dunkirk public prosecutor.
French citizenship minister Marlene Schiappa said she learned of the tragic incident with "great sadness".