North Macedonia called for three days of national mourning after a tourist bus carrying its citizens caught fire and crashed in Bulgaria, killing 46 people in Europe's deadliest road crash in the past decade.

Although the cause has yet to be determined, officials believe the bus crashed into the guardrails and caught fire while returning from Istanbul in Turkey to Skopje in North Macedonia.

Those who died trapped in the burning bus - including four-year-old twins, according to media reports - were mostly from North Macedonia, prompting the government to declare three days of mourning.

The flag of the Republic of North Macedonia will be flown at half-mast. Bulgaria has also declared a day of mourning on Wednesday.

Only four men and three women, including a 16-year-old girl, survived the crash by breaking one of the windows and jumping to safety, according to officials.

Officials believe the bus crashed into the guardrails and caught fire

'Lost my whole family'

"I lost my whole family in the blaze," one man told the Sloboden Pecat newspaper, saying 10 relatives had died.

Media in North Macedonia reported that several of the dead were from a Skopje primary school, where all classes were stopped.

The accident happened after midnight on a highway about 40 kilometres from Sofia, near the village of Bosnek.

Many of the dead were between 20 to 30 years old, officials said.

Local media said the bus was registered with the Besa Trans tourist agency, which organises sightseeing and shopping tours to Istanbul.

It was one of four buses travelling back to Skopje along the same highway at short intervals.

The tour bus company did not immediately respond when contacted by AFP for comment.

North Macedonian Prime Minister Zoran Zaev said 12 of the victims were under the age of 18

'Explosion'

Images showed the carcass of the charred bus after it broke through the highway's central guardrail.

Bulgaria's interim Prime Minister Stefan Yanev said a probe into the accident had been launched, dismissing suggestions that road conditions were to blame.

Deputy chief prosecutor Borislav Sarafov said they were still investigating "if it was a technical fault of the vehicle or a human error that caused the crash".

North Macedonian Prime Minister Zoran Zaev told state news agency MIA that he had spoken to one survivor.

"He explained that they were sleeping in the bus when an explosion was heard. They succeeded in breaking one of the windows and saved a few people. Unfortunately, the rest did not succeed," he said.

Bulgarian national police chief Stanimir Stanev said the bus driver died "immediately so there was no one able to open the doors".

Bulgaria's Interior Minister Boyko Rashkov, who was among those who rushed to the site of the crash, described the scene as "terrifying".

We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences

'Europe stands with you'

Bulgaria has a history of deadly bus accidents, but this disaster is the worst, according to officials.

Twenty Bulgarians died in 2018 when a bus skidded on a wet road and overturned.

EU chief Ursula von der Leyen sent her "deepest condolences to the families and friends of those who perished in the tragic bus accident" and wished "a fast recovery to those injured".

"In these terrible times, Europe stands in solidarity with you," she said.

Russian President Vladimir Putin also expressed his "sincere condolences" and said he hoped for "the speedy recovery of all those wounded".

A total of 628 people died in road accidents in 2019 and 463 in 2020 in Bulgaria, according to official data.

The accidents were often attributed to poor road conditions, outdated cars and speeding.

This accident occurred on a section of highway with steep gradients and without clear demarcation lines.

Many accidents have taken place there in the past, said road safety activist Diana Roussinova, whose organisation has already complained to authorities about the stretch.

In one of Europe's worst accidents in recent years, 43 people died in 2015 when a bus carrying a pensioners' club collided with a lorry and caught fire in southwest France.

In 2010, 45 people died when a train and a bus collided at a crossing in Ukraine.