India is due to test fire a long-range inter-continental ballistic missile capable of carrying nuclear warheads.
The locally-developed Agni-V missile has a range of more than 5,000km (3,100 miles) and is expected to be launched in the eastern state of Orissa.
Analysts say the Agni (meaning "fire" in Hindi and Sanskrit) missile family is to be the cornerstone of India's missile-based nuclear deterrent.
The missiles are among India's most sophisticated weapons.
In 2010, India successfully test-fired Agni-II, an intermediate-range ballistic missile with a range of more than 2,000km (1,250 miles).
Defence analyst Rahul Bedi says the successful test flight of the Agni-V missile, which is capable of delivering a single 1.5-ton warhead deep inside nuclear rival China's territory, will strengthen India's nuclear deterrence once it comes into service by 2014-15.
It is 17.5m-tall, solid-fuelled, has three stages and a launch weight of 50 tons. It has cost more than 2.5bn rupees ($480m; £307m) to develop.
Only China, Russia, France, the US, Great Britain and Israel are thought to have such long-range missiles.
"Agni-V is to meet our present-day threat perceptions, which are determined by our defence forces and other agencies," a spokesman for the Defence Research and Development Organisation (DRDO), Ravi Gupta, told AFP news agency.
"This is a deterrent to avoid wars and it is not country-specific," he said.
Mr Gupta said India "has a no-first-use policy", and described the country's missile development programme "purely defensive".
VK Saraswat, scientific adviser to Defence Minister AK Antony, told The Hindu newspaper that the launch will mark a "historic day".
"Agni-V is a game-changer and a technological marvel. It is a weapon which can perform multiple functions," he said.