South Korean newspapers on Friday urged the government to hit back hard if North Korea strikes again, and blasted China's failure to condemn or restrain its wayward ally.

Thursday's resignation of Defence Minister Kim Tae-Young "should be the starting point for reform of the national security system", the best-selling Chosun Ilbo said in an editorial.

The Seoul administration has come in for stinging criticism that it responded feebly to the North's artillery bombardment Tuesday of a South Korean border island, which killed two marines and two civilians.

Chosun said the South had failed to keep promises of tough retaliation for the North's provocations.

"Kim Jong-Il and his puppets will consider South Korea as nothing but a scarecrow," the paper said.

Dong-A Ilbo said South Korea and the United States "need to awaken North Korea and send them a strong message that if they ever come over the Northern Limit Line (the disputed Yellow Sea border), we will pay them back."

China, the North's sole major ally, has failed to join international condemnation of Pyongyang for the attack.

Dong-A said China's moves were "suspicious", noting that its foreign minister Yang Jiechi had cancelled a trip to South Korea due to start Friday.

"If it (China) ever had any intention of criticising North Korea for its wrongful behaviour, it would not have committed such a diplomatic discourtesy," the paper said.

The Korea Herald questioned whether Beijing, which earlier failed to condemn a March attack on a South Korean warship blamed on the North, has a hidden agenda in its relations with Pyongyang.

"It may not be South Korea alone that believes that China's pampering has emboldened North Korea in its military action against the South," the Herald said.

The Korea Times called on China to "behave as a responsible member of the international community", saying the world's second largest economy must become pro-active regionally and globally.

"This is not the Cold War era but North Korea is still living with a Cold War mentality. Without peace on the Korean peninsula, China's prosperity will also be in jeopardy," the Times said.