A top Communist reformer has called for change in China on the eve of a 10-yearly power handover, saying that reining in the ruling party's unchecked power is the only way to modernise the nation.

Hu Deping, son of former party head and reformer Hu Yaobang -- whose death in 1989 sparked the Tiananmen Square democracy protests -- said the Communists needed to cast off the trappings of China's imperial past and advance constitutional governance.

His comments, carried in the current issue of the respected Economic Observer weekly, come as the party opens its 18th congress Thursday, ushering in a once-in-a-decade leadership transition that will see President Hu Jintao step down as party chief before he retires as president in March.

"There are too many times when power becomes bigger than the law, when the power of the party and government interferes with the judicial process," wrote Hu, who is unrelated to Hu Jintao.

"The basic task of the Chinese Communist Party is to make continuous efforts to advance the establishment and implementation of socialist constitutional government... this is also the demand of the times."

Hu is a leading reformist voice on the Chinese People's Political Consultative Conference, the country's top political advisory body.

His comments express the hopes for political reform of many party insiders, while also echoing the demands of dissidents and rights activists, many of whom have been jailed.

Hu said that 100 years after the Qing Dynasty, China's last imperial ruling house, the Communist Party continued to refuse real constitutional restraints with disastrous results for society and civil rights.

"In the times of an imperial monarchy, there is no constitutional law... the emperor only needs to open his mouth and speak the will of heaven and the state," Hu said.

"The main reason for the disaster of the Cultural Revolution (1966-1976) was because (those in power) ignored, cast aside and destroyed the authority of the constitution... the constitution and law were nothing but empty documents.

"The existence of this kind of behaviour not only harms the healthy development of the state and violates the rights of the people, but also harms the ruling status of the Communist Party."

Hu's father played a major role in leading the party out of the chaos of the Cultural Revolution, rehabilitating hundreds of officials who had been purged and initiating China's period of openness and reform.

He was dismissed as party head in 1987 for reportedly allowing students in Beijing to hold protest marches calling for democratic reforms. Those protests erupted again in 1989 after he died.

Hong Kong newspapers have reported that Hu recently discussed future political reforms with Vice President Xi Jinping, who will be taking over leadership of the party from outgoing President Hu at this week's congress.

During the talks, Xi pledged to advance political reforms, the reports said.

A debate on advancing constitutional democracy in China has been raging among intellectuals and in reformist circles in recent years, leading social critic Yang Jisheng, a retired editor with Xinhua news agency, told AFP.

"This is because there is no balance of power, there are no checks on power," Yang said in an interview.

Reform advocates insist constitutional government should be based on democratic elections.

"If China's state president was elected by the people, then we would have a republic," Bao Tong, a leading dissident and the highest ranking official jailed after the Tiananmen democracy protests, told AFP.

"What is (now) being called a republic, is more of an imperial dynasty than anything else."