The countdown was halted 56 minutes and 24 seconds before the planned liftoff at 2:51 am. Sources said the snag was in the cryogenic stage or last stage of the rocket before it separates. ISRO had announced one hour before launch that the filling of liquid hydrogen fuel had been completed.

"A technical snag was observed in launch vehicle system at 1 hour before the launch. As a measure of abundant precaution, #Chandrayaan2 launch has been called off for today. Revised launch date will be announced later," ISRO tweeted around 3 am.

Ahead of the launch, ISRO chief K Sivan had told NDTV that the space agency has another lift-off opportunity tomorrow if it were called off today. But launch windows have to meet several technical criteria and so it could even take weeks or months for a new date.

"It was the right decision to call off Chandrayaan 2 launch. We could not have taken any chance in such a big mission," former Defence Research and Development Organisation's director of public interface, Ravi Gupta, told news agency ANI.

The 3.8-tonne Chandrayaan 2 spacecraft comprising an orbiter, the lander and the rover was to lift off on the 640-tonne GSLV Mark III (nicknamed "Baahubali"), India's most powerful rocket that's as high as a 15-storey building.

Once it is launched, Chandrayaan 2 has to separate from the rocket and orbit the Earth several times before being slung towards the moon - a 3.84 lakh-km journey. The orbiter is to circle the moon for about a year.

When the spacecraft reaches the moon 54 days after lift-off, it will engage Vikram, a 1.4-tonne lander, which will in turn set the 27-kilogramme rover Pragyan down on a high plain between two craters on the lunar south pole. After touchdown on the moon, the rover is expected to conduct experiments for one Moon day, equal to 14 Earth days, primarily to check if the lunar south pole has primordial water reserves.

The moon mission's success will propel India to an elite league; it would be the fourth country to soft-land a spacecraft on the lunar surface after the US, Russia and China. Israel had tried earlier this year but failed.

All the equipment involved in the Chandrayaan 2 mission have been designed and manufactured in India. It is the sequel to the successful Chandrayaan 1, which helped confirm the presence of water on the moon in 2009.