At least four people tragically lost their lives when a small boat, reportedly filled with migrants, capsized in the frigid waters of the Channel in the early hours of Wednesday morning, the U.K. government declared.

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

U.K. 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."

But the charity Refugee Action said the deaths were "predictable and avoidable," blaming the government for not making safe routes available.

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

Nikolai Posner, from the Utopia 56 group helping migrants in northern France, said they received a voice message and location notification from a boat in distress at 2:53 a.m. local time (1:53 a.m. GMT).

"We forwarded it to the French and British coastguard by phone. At 3:40 a.m., the French coastguard told us the British were handling it," he told Agence France-Presse (AFP).

"The location that was sent to us was in French waters. At 2:59 a.m. 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

The U.K. Maritime and Coastguard Agency (MCA) coordinated the rescue operation, which also involved Border Force, police and other emergency responders.

Lifeboats were launched from the Channel port of Dover at 3:07 a.m. British time (3:07 a.m. GMT), followed by vessels from Ramsgate and Hastings along the coast, it added.

A government spokesperson said the authorities were notified at 3:05 a.m. 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.

The MCA said at least four lifeboats and three coastguard rescue teams were dispatched, as well as two coastguard helicopters. A fishing vessel in the area also helped.

French officials provided a helicopter and a navy patrol boat.

Over 43,000 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 U.K. government, which promised to "take back control" of immigration after its Brexit departure from the European Union.

But opponents have criticized 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 right-winger Braverman, of demonizing 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 those arriving in U.K. 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 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 freezing winter temperatures.