Thousands of miners in China's coal-rich northeast have gone on strike over months of unpaid wages, amid fears of mass layoffs as the government seeks to restructure lumbering state-owned industries.

Social unrest is anathema to China's Communist leaders, making the threat of worker discontent a disincentive to the hard choices analysts see as necessary to reform the world's second-largest economy.

Video seen by AFP Monday showed protesters marching through the streets of Shuangyashan city in Heilongjiang province, venting their frustration at Longmay Mining Holding Group, the biggest coal firm in northeast China.

Pictures showed enormous crowds filling the streets.

"I'm on my knees, my family can't eat," an elderly woman pleaded with a man who appeared to be a government official.

"Tell me, how can we live?" she shouted, before collapsing and being rushed away by fellow protesters.

The situation in Heilongjiang exemplifies the dilemma faced by Chinese authorities, who say they want to change the economic model to one driven by consumer demand rather than infrastructure investment and exports.

China's state-owned enterprises (SOEs) are plagued by overcapacity and many are unviable, but the government has been loathe to kill off such "zombie" companies, fearing unemployment could lead to instability.

Nevertheless, it plans to lay off about 1.8 million workers in the steel and coal industries, a human resources and social security ministry official said last month.

In the video footage from Heilongjiang, dozens of police cars, lights flashing, lined the streets, and protesters complained of violence by authorities as tensions mounted.

"Traffic in the centre of Shuangyashan city was halted," a witness told AFP, adding "some people were hurt".

Pictures from the scene showed what appeared to be police tussling with protesters, with one woman apparently thrown to the ground.

Striking miners held large banners demanding back pay.

"Their main request is to get the delayed incomes from the past several months," the witness said.

The miners' anger spilled into street action after Heilongjiang's governor Lu Hao said the company owed employees no back pay.

At the weekend the provincial government admitted that workers' compensation was in "arrears" following "many years of accumulated problems".

As a result, "not a few workers have encountered difficulties in their lives", it said.

- 'Heavy losses' -

The statement blamed the company's financial woes on inefficiency, saying that it "uses three times as much labour as the national average to produce 10,000 tonnes of coal", resulting in "heavy losses and diminished cash flow".

The firm was "resolutely battling" to implement reforms, it said.

Late last year, 21 miners died in a fire at a mine operated by the company.

Northeast China, a hub for heavy industry, has been particularly hard hit as the country's growth slows, as has the coal industry nationwide.

Consumption of the heavily polluting fuel fell 3.7 percent last year, according to China's National Bureau of Statistics, after a 2.9 percent decrease in 2014.

Coal use is slowing globally and with China's massive production volumes leading a glut in supply, prices have plummeted, falling by more than 50 percent since 2012.

Earlier this month Premier Li Keqiang again pledged to encourage "structural adjustments" in his opening speech to the annual session of China's Communist-controlled parliament.

The country saw at least 1,050 strikes and protests by workers -- around 90 percent of them related to unpaid wages -- in the 10 weeks to the start of the Lunar New Year in February, according to China Labour Bulletin, an overseas campaign group.

"There have been a steadily increasing number of wage arrears protests by coal miners all over China over the last couple of years as the industry contracts and coal prices fall," said its spokesman Geoff Crothall, adding that Longmay miners in another Heilongjiang city protested over the same issue last year.

In Shuangyashan city officials held an emergency meeting on Monday, according to news site Sohu, calling for calm and assuring protestors that the company would "work with all its might to provide workers' wages in a timely fashion".