The Congress and the Bharatiya Janata Party (BJP) will be locked in the biggest popularity test ahead of Lok Sabha polls due next year when Delhi, Rajasthan, Madhya Pradesh, Chhattisgarh and Mizoram vote in November-December.
Announcing the election schedule, Chief Election Commissioner VS Sampath on Friday said the results from the five states - three of them at present ruled by the Congress and two by the BJP - will be out December 8.
While the Congress rules Delhi, Rajasthan and Mizoram, the BJP governs Madhya Pradesh and Chhattisgarh.
Sampath said a total of 110 million electorate - of the country's 714 million - will be eligible to vote in the five states.
Both the BJP and Congress vowed to sweep the polls.
BJP's Sudhanshu Trivedi claimed his party will retain power in Madhya Pradesh and Chhattisgarh and oust the Congress in Delhi and Rajasthan. The mood in the country, he said, "is in favour of BJP".
Rashid Alvi of the Congress said his party was confident of forming governments in all five states.
Political pundits were more guarded.
Experts said it would be a key test for both parties in the run up to the parliamentary elections.
Pradip Kumar Datta of Delhi University's political science department told IANS that the state elections "will be significant, and in a way will be a testing ground for (BJP's prime ministerial candidate Narendra) Modi. Unless the BJP does very well in these polls, it will not be able to attract allies (for Lok Sabha). If the BJP does better than its earlier standing in the five states, it will be a clear demonstration of Modi's vote catching abilities."
Nisar-ul Haq of the political science department of Jamia Millia Islamia, however, predicted "a very close fight between the Congress and BJP".
"It will be major election because it is coming right before the general election," Haq told IANS.
The Election Commission said by-elections will also be held for the assembly constituencies of Surat West in Gujarat and Yercaud in Tamil Nadu on December 4 - along with voting in Delhi and Mizoram.
"All measures are in place to conduct free and fair polls," Sampath said, putting the number of polling stations at 130,000 in the five states.
Thousands of police and paramilitary forces will provide security to the staggered elections.
The balloting in the five states comes at a time when Modi is spearheading a very vocal election campaign for the BJP with 2014 in view.
The Congress and the BJP will be the main players in Delhi (70 seats), Rajasthan (200), Chhattisgarh (90) and Madhya Pradesh (230 seats). Mizoram has a 40-member assembly.
Since its birth last year, the Aam Aadmi Party (AAP) led by activist-turned-politician Arvind Kejriwal has emerged as a key but untested force in the national capital on the strength of its anti-corruption drive.
Delhi University's Datta warned that AAP could wean away a section of the BJP's middle class voters disgusted with corruption as well as the poor who normally vote for the Congress.
Sampath said the model code of conduct, which bars governments from giving away sops to voters, comes into effect immediately.
The Lok Sabha election is due in May 2014, followed quickly by polling in Sikkim, Odisha and Andhra Pradesh. Haryana and Maharashtra are also due to go to the polls next year.
For the first time, voters will have a choice to go for "None of the Above" (NOTA) option on the ballot papers and Electronic Voting Machines if they don't like any of the candidates.
Haq welcomed the introduction of NOTA factor. "It is a good step."