Strikes by thousands of primary and high school teachers over underpaid salaries and a controversial pension system have spread to more cities and counties in Northeast China's Heilongjiang Province since last week, after a similar protest in Zhaodong took place two weeks ago.

Protests by thousands of teachers in Yilan county entered their fifth day after they gathered in front of the county government building on Wednesday. A teacher in Yilan who requested anonymity told the Global Times Sunday that they have not heard of colleagues being arrested or fired.

Strikes have spread to Shuangcheng, Shangzhi cities as well as Yilan, Binxian, Bayan and Fangzheng counties, with teachers demanding a raise in salaries and a halt to pension payments, according to China National Radio (CNR).

Schools, however, pressured teachers against the protests by threatening demotion or dismissal, said several teachers reached by the Global Times.

The protesters raised banners that read, "We are 4,000 Yilan teachers. Return my withheld money!" Classes in many high and primary schools were suspended due to the protests, the teacher said.

"I make fewer than 2,500 yuan ($407) per month after teaching for 25 years," a teacher from Shuangcheng was quoted by CNR as saying.

"The average salary is low. We deserve low-temperature allowance, social welfare and subsidies for missing meals. But we have none of them. Besides, the monthly allowance for class advisors has remained at 14 yuan for 30 years," a retired teacher from Yilan wrote on Sina Weibo on Wednesday.

"We feel sorry for the students, but we have to go on protesting until the government gives us a positive response," the teacher noted, adding that Monday classes will also be suspended.

Education and finance departments in Heilongjiang have set up a work group, trying to meet reasonable requests of teachers as soon as possible, CNR reported.

Previously, the Zhaodong government raised the average monthly salary by 772 yuan to settle the protest.

The provincial press office said the government will consider and respect the appeals in accordance with the law and regulations, but policies like the pension fund remain, news portal china.com.cn reported on Friday.

Heilongjiang employees in public institutions, including public schools and hospitals, have been required to pay part of the pension deposits on their own since 2004 in a pilot project while the pension funds are paid by their employers in most provinces.

The Yilan government has guaranteed the same wages as same-level cities or counties, but it refused to refund the pensions teachers have paid as it claims it's waiting for the central government to decide whether to implement the policy, said the teacher.