President Vladimir Putin's quick-fire push to overhaul Russia's political system has caught the country's opposition off guard, with critics in disarray about how to respond.

After a long New Year's holiday break, Putin unleashed a political storm last week, proposing an overhaul of the Russian constitution that triggered the resignation of the unpopular prime minister Dmitry Medvedev and his government.

Just five days after proposing the changes, Putin had already submitted the amendments to parliament.

Kremlin critics have been unanimous in their hostility to the reform -- with opposition leader Alexei Navalny saying Putin wants to make himself "leader for life" -- but are struggling with how to fight back.

"The opposition, including Navalny, has been caught in the headlights," political analyst and former Kremlin spin doctor Gleb Pavlovsky told AFP, adding that authorities will seek to keep up the pace.

The reforms will transfer some authority to parliament, including the power to choose the prime minister, and strengthen the role of an advisory body called the State Council, potentially headed by Putin.

One frequent speculation is that Putin, 67, could use that position to continue to shape domestic and foreign policy after his fourth Kremlin term expires in 2024.

But much remains unclear about how the new system would work and why Putin is proposing it now, making it more difficult for opponents of the plan.

"It's perhaps the first time that I don't understand Putin's internal logic," said former opposition lawmaker Gennady Gudkov.

"I just cannot understand why there was such a mad rush."

Some in the opposition, like the liberal Yabloko party, have said they will prepare alternative proposals to reform the constitution, which was adopted under Boris Yeltsin in 1993.

Others -- including Navalny -- seem at a loss.

"No one understands what is going on," the 43-year-old said on his blog this week. "Nothing. Is clear. At all."

"Life will clarify our tactics in the near future," he added.

What is clear is that the process is moving quickly.

Lawmakers in the State Duma -- dominated by the ruling United Russia party -- have already begun studying the proposals and talked of approving the amendments within weeks.

Authorities have promised a public vote on the reform, with some suggesting it could take place before the end of April.

Critics say the Kremlin is looking to push through the legislation in record time to preempt any criticism and avoid potential street protests.

Over his 20 years in power Putin has muzzled independent media and neutered the opposition, while law enforcement agencies have arrested and intimidated activists.

Anti-government protests -- including major demonstrations led by Navalny in 2011-12 -- have ended in crackdowns, with protesters arrested and in some cases sentenced to lengthy jail terms.

A march on Sunday saw fewer than 1,500 people take to the streets of Moscow to protest against political repression.

Navalny's ally Ilya Yashin has said the opposition wants to hold a big rally on February 29 to oppose Putin's reforms, but by then the legislation may have already sailed through the key second reading in parliament's lower house.

Analysts say the speed with which authorities are moving is dangerous because such fundamental changes to the country's governance structure and legislation should not be rushed.

The Kremlin put together a 75-member group to help develop the constitutional amendments but critics called it a farce since Putin has already proposed the changes he wants.

"Everything that is happening is a humiliation of both the constitution and society," said Lev Shlosberg, a regional Yabloko lawmaker from the northwestern city of Pskov, calling Putin's plan a "blitzkrieg".

The reform of the role of the State Council especially has come under fire, with some comparing it to the Soviet-era Politburo, the Communist Party body that effectively ran the country.

Self-exiled Kremlin critic Mikhail Khodorkovsky likened the changes to a Mafia-style succession plan.

"What is happening is the life-long preservation of a system that will ensure the irremovability from office of Putin's gang," he said on Facebook.

Russia Dmitry Medvedev Facebook Vladimir putin