At least six people were killed when a boat carrying migrants heading to Britain sank in the Channel early Saturday, French maritime officials said, as a search continued to find those still missing.

A spokeswoman from the French coastal authority Premar said between five and 10 passengers were still missing, while 55 had been rescued.

Four French ships and a helicopter plus two British vessels were involved in the rescue effort off Sangatte in northern France, authorities said, adding that some survivors were rescued by the British vessels.

Earlier officials had reported that one man of Afghan origin was killed and five others were in critical condition.

A maritime surveillance plane is also being deployed to the area, the Premar spokesman told AFP.

Some of those rescued were taken to the French port of Calais, where an AFP reporter saw people disembarking from a patrol boat with emergency services on site.

More than 100,000 migrants have crossed the English Channel on small boats from France to southeast England since Britain began publicly recording the arrivals in 2018, official figures revealed on Friday.

Read: Pakistanis were forced into lower deck of migrant boat: reports

French authorities have stepped up patrols and other deterrent measures after London agreed in March to send Paris hundreds of millions of euros annually towards the effort.

The route across one of the world’s busiest shipping lanes has repeatedly proved perilous, with several capsizings and scores of migrants drowning in the waters over the last decade.

Five migrants died at sea and four went missing while trying to cross over to Britain from France last year.

In November 2021, 27 migrants died in a boat capsize in the Channel.

This is the second such incident in a single day as two Tunisians including a baby died earlier when their boat sank soon after leaving the country’s shores, the coastguard said, amid a spike in attempts to reach Europe.

The vessel carrying 20 Tunisians went down at 2:00 am when it was only 120 metres (395 feet) from the coast in Gabes, the North African country’s coastguard said.