A fire at a bar in a Swiss ski resort appears to have been caused by sparklers placed on bottles of champagne that came “too close to the ceiling”, authorities said.

Forty people died after the blaze in the early hours of New Year’s Day in Crans-Montana, while 119 were injured.

Valais Attorney General Beatrice Pilloud told a news conference on Friday the investigation would focus on the materials used on the site, the bar’s fire safety measures, its capacity and the number of people inside at the time of the fire.

The investigation will explore whether prosecutions will be necessary. “If that is the case, and if those people are still alive, there will be a case opened against them,” she said.

“Everything leads us to think that the fire started from sparkling candles – or sparklers – which were put on bottles of champagne [that were] moved too close to the ceiling. From that, a blaze began very quickly”, Ms Pilloud told the conference.

One of the bar’s owners reportedly told local media the establishment had been inspected three times in the past ten years and that everything had been done according to the regulations.

Authorities are still working on the formal identification of the 40 people killed in the fire, with police commander Frédéric Gisler saying “that is our priority”.

Many of those injured in the fire remain in a critical condition and “are still fighting to live”, Mathias Reynard, president of the Valais region, said.

Of those injured, 113 have been formally identified, Gisler said. This figure includes 71 Swiss citizens, 14 French, and 11 Italians, as well as four Serbs, among others.

The formal identification process of six others was ongoing, he said, and warned the figures may still change.

Reynard said around 50 injured people “have been transferred or will be transferred soon to European countries in specialised centres for severe burns”.

Among those injured was 19-year-old French footballer Tahirys Dos Santos, according to a statement released by his football club, FC Mertz.

Dos Santos was “severely burned” in the fire, the club said, and has been airlifted to Germany for treatment.

The families of those missing after the fire were still anxiously awaiting updates from officials on Friday evening.

Among those missing is Italian national Achille Barosi, 16, who entered the bar at 01:30 local time on New Year’s Day to retrieve his jacket and phone. His family have not heard from him since.

“We don’t know if he’s still alive,” his aunt Francesca told the BBC World Service’s OS programme. She said her nephew was an excellent painter who had enrolled in an art school in Milan.

At the news conference on Friday, officials said they were identifying victims using a process called “Disaster Victim Identification”, whereby a team of forensic specialists, doctors, dentists and investigators gather data that allows them to name the dead.

Ms Pilloud later told the news conference the investigation would also explore whether the bar ceiling complied with building regulations.

She said investigators were exploring the installation of foam in the ceiling, adding she was unable to say with certainty at this stage whether the foam did or did not comply, or if it was installed with or without authorisation.

“It’s essential we don’t make any assumptions… leave us to do our work,” she said.

She said the two French managers of the bar had been interviewed, as well as people who escaped the fire.

Ms Pilloud said the interviews had helped them to establish a list of those who were present during the incident.

Officials also confirmed there was more than one exit out of the bar, but added they were “not currently able to say” whether the emergency exit was open or closed at the time.

Lea Zehnder, 22, was celebrating New Year’s at a bar within eye-shot of Le Constellation.

She described hearing screams coming from Le Constellation and said her boyfriend helped those with serious burns.

“They couldn’t walk or talk”, she said.

Meanwhile, Tristan Fischer, 20, told the BBC his 17-year-old brother had smashed windows and grabbed people from the bar as the fire took hold.

He said he was worried his brother’s mental health has been permanently affected by the incident: “He hasn’t properly spoken, he hasn’t properly slept since.”

Le Constellation is a large bar which has been around for many years.

It could hold up to 300 people and had a small terrace, although it is unknown how many people were there at the time of the fire.

On Friday, groups of tearful families and teenagers gathered near the police cordon around the bar.

Some left bunches of flowers and candles, while others placed messages at a makeshift shrine.

White tents covered the entrances and exits of the site.

Just outside town, a conference centre is being used to provide support to the families of the missing.

A ceremony will be held in Crans-Montana on 9 January so people can come together for a moment of “national mourning”.