In grainy photographs shot from a plane circling overhead, four people adrift in an iron boat in an expanse of the Mediterranean Sea wave their arms in distress.

It later emerges that the group – a 13-year-old boy, two men and a woman – are the only survivors of a shipwreck that they say killed the other 41 people they were travelling with.

The four survived by floating with inner tubes and lifejackets until they found another empty boat, likely from a previous migrant crossing, and clambered in. They spent several days drifting before being rescued.

A day after news of the tragedy emerged, migrants in the Tunisian city of Sfax prepared to make the same crossing.

One man, who had fled fighting in Sudan’s western region of Darfur, told BBC Arabic that he planned to seek asylum in Tunisia, but was ready to board a boat if this didn’t work. “I just survived a war, I have nothing to lose,” he said. Another, from Kenya, dreamed of a better life for his family in Europe.

If they go ahead with the journeys, the two men will join thousands of others who have risked their lives this year on what has been dubbed the world’s most dangerous migration route.

Experts told the BBC that badly designed and overcrowded boats, stormy weather, and gaps in international efforts were all factors in the danger – and one search-and-rescue NGO described the central Mediterranean as a “cemetery”.

It may feel like you are seeing more reports of shipwrecks this year in the central Mediterranean – and both crossings and deaths do appear to be on the rise.

European border agency Frontex says the central Mediterranean is the “most active route” into the European Union, with more than 89,000 detections reported by national authorities in the first seven months of 2023 – more than double last year, and the highest on record since 2017.

People making the journey set sail from the shores of North Africa, usually for Italy.

The International Organization for Migration (IOM) has recorded more than 1,800 migrant deaths in the central Mediterranean so far this year, compared to 1,400 for the whole of 2022.

Among the migrant shipwrecks this year was an overcrowded fishing vessel off the coast of Greece, which killed hundreds in one of the worst humanitarian disasters in the Mediterranean in recent years.

The IOM says there is strong evidence that many shipwrecks are “invisible”: unrecorded boats disappearing with no survivors, meaning the real death toll is likely to be much higher.

Those embarking on the perilous voyage come from around the world and have various reasons for wanting to reach Europe, from fleeing war or torture, to searching for jobs.

After being rescued from an overcrowded rubber raft this summer, one 16-year-old boy from The Gambia told the BBC he left home three years ago to “hustle hard and help my family”.

He was aware of how dangerous the journey was, having lost an 18-year-old friend to the crossing. But he said this did not deter him – his friend had “lost his life for his family and his society and his nation”.

This year, Tunisia has overtaken Libya as the main point of departure – amid a wave of racism against black Africans there.

Some say the Libya crossing remains more dangerous, both for geographical and political reasons.

“In terms of fatalities, I think that the opening up of the Eastern Libya route (from territories controlled by Wagner-supported militias) is having a bigger impact,” said Nando Sigona, a professor at the University of Birmingham and a migration expert.

“It is much longer and it also brings boats at the border between Italian and Greek national waters – two governments currently not too keen to be seen as providing rescue operations to migrants at sea,” he said, pointing to the Greek shipwreck in June as an example.

Migrants are typically travelling on overcrowded and unseaworthy boats, with limited flotation devices should they capsize.

Types of boats include rubber rafts and fishing vessels – and on the Tunisian route, metal boats are common.

Frontex spokesperson Chris Borowski described them as “coffins in water”.

“Combine this with the fact that usually there are dozens of these launched at one time with 40 or more people on board and you have a recipe for disaster,” he said.

Mr Borowski said that “greedy people smugglers” used metal boats to offer “discount” crossings as they competed for migrants’ business.

Crossings of the central Mediterranean are seasonal, with increased attempts in the summer. But weather can be unpredictable and successful journeys across the Mediterranean can take days.

“If storms occur or the seas are rough – which may become more frequent with climate change – there is a much greater risk to life,” IOM spokesperson Ryan Schroeder said.

“Sometimes not even bad weather deters smugglers from sending people out to sea,” he added, pointing to the boats that have recently capsized near the island of Lampedusa, which were launched despite rough seas.

And Mr Borowski says poor weather makes spotting boats in distress even more difficult.

“Imagine searching for a Vauxhall Corsa from the air in an area the size of the UK. Now try looking for a dozen or more in the open sea,” he said. “This is the daunting challenge in the central Med. This combined with an unforgiving sea, especially when the weather turns bad, as we have seen in recent days.”

While Frontex offers “general oversight and technical support”, Prof Sigona says national governments mostly govern search and rescue (SAR) operations in the central Mediterranean, with the work of NGO vessels closely regulated.

The IOM’s Mr Schroeder said SAR efforts are no longer as “proactive, comprehensive or adequately resourced” as they were during the big Mare Nostrum rescue operation led by Italy in 2013 to 2014.

Under the current system, Mr Schroeder said the IOM was concerned that “SAR gaps, alleged delays in rescue and reported lack of response to distress calls may be contributing to tragedies on this route”.

NGOs operating rescue vessels on the central Mediterranean were more critical. The route “has become so deadly because of a reckless policy of deterrence and neglect that European states have been pursuing for years”, Wasil Schauseil, communications coordinator at SOS Humanity, said.

German NGO Sea-Watch said the EU had “willingly created a cemetery”. It said there was a lack of SAR coordination and that “illegal pullbacks” were being conducted by the Libyan coastguard, which the EU has equipped and trained.

And last month, the EU signed a $118m (£90m) deal with Tunisia to try to reduce “irregular” migration.

A European Commission spokesperson defended working with the North African countries, saying the “still too high number of casualties” in the Mediterranean meant it was “important to continue strengthening the capacity of the Libyan coastal authorities to carry out effective search and rescue operations in line with international standards”.

NGOs have also criticised a new law in Italy requiring their rescue vessels to head to often distant ports after an operation rather than continuing to patrol for more migrant boats in distress. They say this reduces their time in areas were shipwrecks are more common.

Italy says the aim is to spread arrivals across the country.

Critics of rescue NGOs say their presence encourages migrants to embark on the potentially fatal journey – the NGOs reject this.

Frontex’s Mr Borowski acknowledged that “we can, and indeed, we must, do better” at stopping “tragedies at sea”, calling for “shared solutions”. IOM spokesperson Mr Schroeder said all efforts should “focus on saving lives and addressing the reasons that people are compelled to risk their lives”.

The IOM and other UN agencies have called for coordinated European search-and-rescue operations in the central Mediterranean, and for safer legal pathways for migration and asylum to prevent deaths at sea.

The European Commission spokesperson said its efforts to enhance SAR coordination between its members were “extensive”. It was working to deter smugglers and develop safe ways for people to come to the EU that would break “the business model of the smugglers and the traffickers”.

They said shipwrecks, like the one this summer off the coast of Greece, are “yet another call to action” that highlighted “the urgency to intensify our work”.

Additional reporting by Bassam Bounenni, BBC Arabic