London (AFP) - At least four people died when a small boat apparently packed with migrants capsized in freezing temperatures in the Channel overnight, the UK government said on Wednesday.

Dozens of others were plucked from the waters of one of the world’s busiest shipping lanes in a large-scale rescue operation involving UK and French emergency services.

Prime Minister Rishi Sunak, who is trying to tighten rules to prevent record numbers of migrants from attempting the crossing, called the capsize a “tragic loss of human life”.

Interior minister Suella Braverman said the fatalities – and the loss of 27 lives in November last year – were “the most sobering reminder” of the need to cut off the route.

“Crossing the Channel in unseaworthy vessels is lethally dangerous,” she told parliament, promising closer cooperation with the French authorities.

“It is for this reason above all that we are trying to destroy the business model of the people smugglers.”

The charity Refugee Action said the deaths were “predictable and avoidable”, while the Care4Calais group called the UK government’s failure to make safe routes available “utterly shameful”.

Sunak’s spokesman dismissed such criticisms as inappropriate.

“The government is firmly fixed on resolving this issue,” he told reporters.

Ministers are acting to end “vulnerable people being exploited”, while Britain has accepted hundreds of thousands of individuals through safe routes over a number of years, he added.

Government sources said earlier that 43 people were rescued, including more than 30 who had fallen overboard, with fears the death toll will rise.

- Scream for help -

A fisherman told Sky News he was awoken by his crew reporting screams for help from migrants aboard a stricken inflatable vessel and in the near-freezing water next to their trawler.

The crew spent several hours plucking dozens to safety, sharing footage of the dramatic scene with the UK broadcaster, comparing it to scenes from a war movie.

“Adrenaline kicks in and you find the strength to get these guys safe,” the fisherman, named only as Raymond, said.

Nikolai Posner, from the Utopia 56 group helping migrants in northern France, said it received a voice message and location notification from a boat in distress at 2:53 am local time (0153 GMT).

“We forwarded it to the French and British coastguard by phone. At 3:40 am (0240 GMT), the French coastguard told us the British were handling it,” he told AFP.

“The location that was sent to us was in French waters. At 2:59 am the person who contacted us was no longer receiving messages on WhatsApp.”

Posner, however, said he could not be sure if the message originated from the same small boat.

- Lifeboats, helicopters -

The UK Maritime and Coastguard Agency (MCA) coordinated the rescue operation, dispatching four lifeboats, three coastguard rescue teams and two helicopters.

French officials also provided a helicopter and a navy patrol boat.

A government spokesman said the authorities were notified at 3:05 am about “a migrant small boat in distress”.

“There have been four confirmed deaths as a result of this incident, investigations are ongoing and we will provide further information in due course,” he added.

More than 44,000 migrants have made the journey across the Channel so far this year – a record – creating tensions between London and Paris about tougher preventative measures.

It has also piled political pressure on the UK government, which promised to “take back control” of immigration after its Brexit departure from the European Union.

Opponents have criticised the government’s attempts to tighten entry rules and called its proposals to deport failed asylum seekers to Rwanda unlawful.

They have also accused ministers, including Braverman, of demonising asylum seekers and fuelling hostility towards people seeking sanctuary with inflammatory rhetoric.

On Tuesday, Sunak announced a new deal with Albania to stem the flow of migrants crossing the Channel from mainland Europe.

A third of all those arriving in UK waters this year – almost 13,000 – have been Albanian.

Under the agreement, Albanians arriving by boat across the Channel would be immediately returned to their home country.

Freezing weather conditions in northern Europe and high winds on the Channel have deterred crossings in recent days.

But a drop in the wind appears to have prompted the latest attempt, despite increased risks of hypothermia during icy winter temperatures.