Bucharest (AFP) - The majority of miners who have been on strike in Romania since 11 January have agreed to go to back to work after winning wage rises, the country's energy ministry said on Thursday.

The strike has sparked fears of power shortages after one of Romania's main electricity plants began shutting down on Thursday due to insufficient coal supplies.

But workers in seven of the ten mines where wildcat strikes had been taking place "have agreed to return to work," the ministry said after negotiations.

However, unions sounded a more cautious note about the agreement, which will see workers' net salaries -- on average 500 euros -- rise by 137 euros (585 lei) a month.

The agreement also includes an annual holiday bonus of 300 euros.

"Some of the miners are disappointed because they had asked for a raise of 220 euros a month," union official Nicu Bunoaica told AFP, emphasising that the deal still had to be scrutinised by workers at each of the ten mines.

Around 7,000 miners in total have been on strike in the CEO Oltenia combine in the south of the country.

As a result, the first of three units at one of Romania's main electricity plants was shut down overnight, operator Transelectrica said in a statement.

To make up for possible shortages, Bucharest has increased electricity imports in recent days but at prices well above those of local power producers.

Prime Minister Viorica Dancila had called the situation "very serious" while Energy Minister Anton Anton said the current strike had added to existing doubts about CEO Oltenia's profitability.

"If work doesn't restart today (Thursday), it would be hard for me to say what the combine's future would be," Anton said.

CEO Oltenia generates around 30 percent of Romania's electricity needs but ran up losses of around one billion lei (213 million euros) in 2018 as coal mining becomes less profitable.

Romania, which joined the European Union in 2007, has promised Brussels it will gradually close its coal mines and turn to non-polluting sources of energy.

But in recent years, Bucharest has asked to postpone the closures in order to limit lay-offs of miners.