The factory makes exhaust systems for Guangqi Honda Automobile. A spokesman for Honda Motor (China) said yesterday that all assembly lines at its plants in Huangpu and Zengcheng , which employ about 6,000 workers, would halt production today due to a lack of parts.

The recent incidents of labour unrest come against a broader backdrop of rising labour costs and growing worker agitation in the mainland's main manufacturing hubs. Electronics giant Foxconn has been forced to raise salaries after a rash of suicides in Shenzhen, and workers at a Honda Autoparts Manufacturing plant in Foshan won a pay rise on Friday after a two-week strike.

Geoffrey Crothall, a spokesman for the Hong Kong-based group China Labour Bulletin, said the clashes appeared to be part of a pattern.

'There has definitely been an upsurge in worker discontent and activism this year,' he said. 'It isn't just in southern China. We are seeing it in central provinces and now in the Yangtze River Delta. And it is not just the young - middle-aged workers are now beginning to say 'enough is enough, give us our due'.'

He said worker activism tended to come in waves. There was a big surge in 2008 but things went relatively quiet last year due to the economic downturn.

'As things begin to improve and orders are now starting to pick up again, workers are quite rightly wanting their fair share of the profits. As long as workers are being paid ridiculously low wages that can't even provide basic subsistence living costs, then they are going to start standing up for themselves.'

Workers at the Taiwanese-owned KOK International plant in Kunshan , Jiangsu , accused the authorities of colluding with their employer and using violence to break up a protest over work conditions and pay.

'The police beat us indiscriminately,' one young woman worker said. 'They kicked and stomped on everybody, no matter whether they were male or female.

'I saw several riot police beating one worker who had fallen on the ground, then they dragged him away into their van.'

Other workers said about 50 protesters had been injured in the confrontation, which lasted about an hour, and 30 to 40 had been arrested. One of those who had been hurt and taken away was said to be pregnant. They said between seven and 10 of their colleagues remained in police custody and were expected to be held for 15 days.

The clashes apparently took place when the protest spilled out onto the main road outside the factory. However, staff insisted they were 'just standing at the gate'.

The dispute - which workers said began on Friday with near-unanimous support - concerns conditions that employees say are unbearable, enforced unpaid overtime and low pay, the firm's alleged non-payment of social security and a lack of cover for work-related injuries.

'We have to work in temperatures of 40 to 50 degrees Celsius,' one migrant worker from Yunnan said. 'They refuse to do anything about the heat. The smell from the rubber is unbearable, but we don't even get a toxic fumes subsidy. If we get hurt at work they actually dock time out of our pay. Basic pay last month was supposed to be 960 yuan (HK$1,100), but I was only paid 903 yuan. How can we survive on this?'

KOK refused to allow a South China Morning Post reporter into the dusty white factory's rundown compound yesterday and turned down requests for an interview. About a dozen plain-clothes and uniformed police, plus security guards and some local government officials were stationed outside the gates.

On hearing of a media audience, striking staff crowded at windows, shouted and waved from the rooftop and crammed behind the plant's gate, calling out complaints. At one point two women workers sneaked out and tried to approach the Post reporter but they were pushed back inside by security guards.

Lu Quanyuan , a local government spokesman and director of the Huaqiao Economic Development Zone Personnel Bureau, said it was a 'simple case of employer-staff conflict', which officials aimed to resolve at the earliest opportunity.

'The company demanded on June 3 that staff sign a new contract, backdated to February 1, and which was in breach of some of their labour rights,' he said. 'We immediately got involved to mediate to protect workers' basic rights.'

He said the majority of issues had been resolved while a few minor points were still being negotiated.

Workers later said that nothing has been sorted out.

Lu was evasive when asked about arrests and declined to address the issue of whether anyone had been hurt. 'I think the police, in order to maintain traffic safety, may have ... well, I didn't see it myself. I think they asked workers to go back inside.'

Chen Weihua , who manages a firm in the same street, said he saw 100 to 200 workers blocking the main entrance after 10am on Monday, with about 20 black-clad riot police officers watching them closely.

One striker who was taken away by police for seven hours on Monday to 'co-operate with their investigation' said he had been treated as a criminal for complaining about lack of insurance and being underpaid.

Trying times

Recent strikes at mainland factories

Foshan: Honda workers clash with riot police on May 31

Foshan: 250 workers at Guangqi Honda strike on Monday

Dongguan: Workers at shoe factory strike on Friday

Kunshan: 2,000 workers at KOK factory clash with riot police on Monday

Huizhou: 2,000 employees of Yacheng Electronics strike on Monday

Shenzhen: Workers at Merry Electronics Co protest on Sunday

SOURCE: SCMP