BEIJING -- Two state policy-backed banks vowed Thursday to keep holding shares to stabilize the stock market after violent fluctuations.

China Development Bank announced that its subsidiaries will keep and buy shares while the Export-Import Bank of China pledged to ask funds and investment firms it has invested in to keep and buy shares.

Five state banks including Bank of China and Bank of Agriculture and some joint-stock banks vowed not to sell shares on Wednesday.

The stock market took a nosedive over the last month, with the Shanghai Composite Index shedding about 30 percent. Chinese shares surged nearly 6 percent at closing Thursday after a string of stabilizing measures.