China could see a repeat of the Cultural Revolution's deadly chaos without "urgent" political reform, Wen Jiabao warned Wednesday in a dramatic parting shot at his final news conference as premier.

Wen is widely considered the most progressive of China's leaders, but analysts said the comments, at the closing of the annual parliamentary session, were his strongest call yet for political reform in the one-party state.

"We must press ahead with both economic structural reform and political structural reform, in particular reform in the leadership system of our party and country," he told reporters, adding it was an "urgent task".

"Without a successful political structural reform, it is impossible for us to fully institute economic structural reform and the gains we have made in this area may be lost," he said.

"Such historical tragedy as the Cultural Revolution may happen again."

The 1966-1976 Cultural Revolution was a decade of brutal chaos launched by revolutionary leader Mao Zedong to bring down what he perceived as "capitalist" forces.

Untold numbers died in the turmoil as students turned on teachers and officials were purged, and that period still haunts the older Chinese generation today.

Wen's comments came after China's parliament passed into law changes to the criminal law that give police the power to detain some suspects in secret locations known as "black jails".

The 3,000 members of the National People's Congress (NPC) voted overwhelmingly in favour of the legal amendments, which have been widely criticised.

But experts said an eleventh-hour change to the bill obliging police to inform relatives of those placed in informal detention within 24 hours was a victory for legal reformists.

It is the last time Wen will speak at the parliament's closing press conference -- his successor will be appointed at the 2013 NPC -- and the premier was visibly emotional.

"The reference to the risk of a new Cultural Revolution is the strongest statement ever made by Wen Jiabao on the urgency of carrying out political reforms," said Nicholas Bequelin, senior Asia researcher at Human Rights Watch.

"By political reforms he doesn't mean democratisation but rather a series of reforms that go beyond technocratic tinkering -- establishing a real rule of law, enfranchising workers."

Wen is the only leader to have repeatedly spoken of the need for political reform in China, although critics have accused him of paying lip service to the issue.

Wen also hinted at the need to give people more of a say in the one-party state, saying villagers had the right to direct elections at the local-level.

But China's ruling Communist Party -- which controls the army and the government -- maintains an iron grip on political power, and other leaders have in the past ruled out any shift to multi-party democracy.

Analysts also said Wen's warning on the Cultural Revolution could be an oblique criticism of Bo Xilai, head of the southwestern city of Chongqing, who has launched a Maoist revival campaign that has sparked concern among liberals.

Many believe Bo is angling for a place on the party's nine-member standing committee -- the top organ of power -- when a leadership transition begins later this year, but he has since become embroiled in a high-profile scandal.

Wang Lijun, his former police chief, reportedly attempted to defect to the United States last month and was then detained -- a rare, open political drama that Wen said officials must "learn lessons" from.

Analysts said Wen's comments on the importance of reforming China's leadership may also be a thinly-veiled criticism of the party's huge power in the country.

"The subtext is that the party has too much power, the party is interfering in the work of the government," said Willy Lam, a leading China expert at the Chinese University of Hong Kong.

"He wants to reiterate the importance of separation of power and government."

Asked about the conflict in Syria, Wen said that Arab people's demands for democracy "must be respected and truly responded to".

Beijing has been condemned for vetoing two UN resolutions urging an end to the crackdown on a Syrian democracy protest movement that began during the Arab Spring uprisings last year.

The Chinese government fears this movement, and last year cracked down hard on dissidents and rights lawyers when anonymous calls emerged online calling for similar demonstrations in China.

Wen also touched on the economy -- part of his portfolio -- saying among other things that China's yuan was close to reaching a balanced level and vowing to improve the flexibility of the currency.