About 100 people are feared to have drowned off the coast of Libya after their smuggler abandoned them on the high seas without a motor, increasing the Mediterranean death toll this year to an unprecedented 4,700.

The toll is now over 20% higher than last year’s total of 3,771, which was the previous annual record.

A boat containing about 130 refugees sank in the early hours of Thursday morning, killing about 100 people, some of the 27 survivors told Médecins Sans Frontières (MSF), the medical charity now transporting them to Italy. Just seven bodies were recovered.

The inflatable boat sank after smugglers, who had towed the dinghy out to sea, returned to land with its engine and the migrants’ lifejackets, several survivors told MSF.

Abdoullae Diallo, an 18-year-old from Senegal, was quoted as saying: “At that moment I thought we were going to die. I knew we were not close to Italy and without an engine we could not get far. The smuggler told us we would be rescued, but I felt we were going to die.”

The events highlight the catch-22 facing the European rescue missions operating off the Libyan coast.

The vast majority of migrants are now sent to sea by smugglers without enough fuel or equipment to reach Italy, in the expectation that they will be rescued by the charities, navies and merchant ships sailing in the area. But when rescue missions were suspended in early 2015, in the belief that they were actively encouraging more people to put their lives at risk, more migrants came than ever before, and more of them drowned.

Refugee advocates such as MSF argue that the only effective response is to increase the number of legal routes available to migrants considering putting their lives at risk at sea.

Ed Taylor, a rescue worker who returned this week from four months onboard an MSF boat, said: “Europe cannot continue to pretend this isn’t happening. There is an urgent need for safe and legal ways to seek safety in Europe. Without them, and with such a focus on anti-smuggling operations, people are risking their lives in increasingly dangerous crossings as smugglers resort to progressively more inhumane acts.”

The 27 men now on board the #Argos were on board a boat carrying 130 #people. They are the only survivors. This tragedy is just unbareable. pic.twitter.com/vWLaGoUCzt — MSF Sea (@MSF_Sea) November 17, 2016

So many people have now drowned in the Mediterranean in 2016 that the final death toll could conceivably exceed not just the Mediterranean record, but last year’s global record of 5,729.

The high death rate is partly due to unusually high migration flows from Libya in October and November, months when departures usually tail off due to worsening weather.

While migration levels between Turkey and Greece have fallen significantly since March, after Turkey agreed to readmit people deported from Greece, crossings between Libya and Italy continue unabated. Over 167,000 people have reached Italy so far this year from north Africa, and the final annual total is likely to surpass the previous record of 170,000.

European countries are attempting to stem migration flows by providing more aid to African countries that agree to readmit deported asylum seekers. Additionally, navies from countries such as Britain are intercepting and destroying Libyan smugglers’ repurposed fishing trawlers after they enter international waters.

But the strategy has failed because the smugglers have instead packed their customers into disposable rubber boats instead. These can be driven by the refugees themselves, allowing the smugglers to remain at large in Libya. These inflatable boats are even more dangerous than the wooden ships they replaced.

Syrians are no longer using Libya as a springboard to reach Europe. Instead, Libya is mainly used by people fleeing war and poverty in Nigeria and Sudan, or repression in Eritrea and the Gambia. Others taking to the sea are migrant workers who tried to find jobs in Libya, but are fleeing after the Libyan civil war led to the collapse of law and order.

Many migrants are kept in slavery-like conditions by their Libyan employers, while others are tortured or extorted, sometimes by the authorities. Around 70% say they faced some kind of exploitation in Libya, according to research by the International Organisation for Migration.