Thirty people have died after a migrant boat headed for the UK capsized in the English Channel.

Prime Minister Boris Johnson said he was “shocked, appalled and deeply saddened” to hear of the loss of life.

France’s prime minister said the shipwreck on Wednesday was a “tragedy” and his thoughts were with “victims of criminal smugglers who exploit their distress and injury”.

While the total number of deaths is unclear, the president and chairman of the ports of Calais and Boulogne reported that 30 people had died.

French politician Franck Dhersin said on Twitter that a boat with more than 50 people aboard had sunk in the middle of the Channel.

He reported that at least 24 people had died in the capsizing while others had survived.

A rescue operation is under way in the Channel by air and sea as French and British authorities search for anyone still in the water.

Mr Johnson will chair a meeting of the Cobra emergency committee in response to the incident, Downing Street said.

The emergency search was sparked when a fishing boat sounded the alarm earlier on Wednesday after spotting several people at sea off the coast of France.

French prime minister Jean Castex said: “My thoughts are with the many missing and injured, victims of criminal smugglers who exploit their distress and injury.”

French interior minister Gerald Darmanin confirmed on Twitter that people had died but did not give a number.

Dover MP Natalie Elphicke said: “This is an absolute tragedy. It underlines why saving lives at sea starts by stopping the boats entering the water in the first place.

“As winter is approaching the seas will get rougher, the water colder, the risk of even more lives tragically being lost greater.

“That’s why stopping these dangerous crossings is the humanitarian and right thing to do.”

The deaths come amid continued spotlight on Home Secretary Priti Patel and the Government as thousands of people still risk their lives on the perilous route.

A number of people are also believed to have reached Britain in small boats on Wednesday, with people seen being brought ashore in Dover by immigration officials.

The Dover Strait is the busiest shipping lane in the world and has claimed many lives of people trying to cross to Britain in inflatable dinghies.

Enver Solomon, chief executive of the Refugee Council, said: “It’s heartbreaking to hear that the lives of more ordinary people have been lost on a harrowing journey to Britain in search of safety.

“How many tragedies like this must we see before the Government fundamentally changes its approach by committing to an ambitious expansion of safe routes for those men, women and children in desperate need of protection?

“Every day, people are forced to flee their home through no fault of their own. Now is the time to end the cruel and ineffective tactic of seeking to punish or push away those who try and find safety in our country.”

More than 25,700 people have made the dangerous journey to the UK in small boats this year – three times the total for the whole of 2020, according to data compiled by the PA news agency.