Slovenia observed a national day of mourning on 24 January for three miners who died in an inrush of clay in the Velenje coal mine, the country's deadliest coal mining accident in more than two decades.

Flags on all state institutions were at half mast and organisers of events around the country as well as public media adjusted their programming.

Locals paid their respects to the dead miners at a monument to a miner at the city's central Tito Square, and a special commemoration was held at the Velenje Culture House featuring local and government officials, and employees of the coal mine.

Velenje Mayor Peter Dermol said that the people of Velenje have shown mining is in their hearts.

"It's our responsibility to pay tribute to the people who gave their lives so that we have electricity, that's what is important at this moment," he said in reference to the coal from the mine being used by the power station in nearby Šoštanj.

"A dignified farewell is what our three heroes need and what their families deserve," he added, pledging that the city will help their families.

The accident has led to an outpur of support. The government and the coal mine operator have pledged to provide financial aid to the families of the three miners, aged 31, 32 and 49, and a national fundraising campaign has been launched by the coal mining trade union.

"As miners, we are aware that we have a duty of care to the families of our deceased colleagues," the trade union and the works council said in a joint statement.

The deadliest coal mining accident in Slovenia in more than two decades happened when an estimated 700 cubic metres of clay collapsed on an extraction site 500 metres below ground.

While a dozen miners were able to escape unharmed, three died under the clay. One body was recovered just hours after the accident and two were found two days later.

The cause of the accident is still being investigated.

Velenje is the only operational coal mine in the country. It produces lignite, a low-quality coal, that is burned in the nearby Šoštanj power plant. Both the coal mine and the power plant will be phased out by 2033 at the latest but likely much earlier.