The launch of India's second lunar mission has been halted less than an hour before the scheduled blast-off, due to a technical problem.
The countdown stopped 56 minutes before the launch after a "technical snag was observed in launch vehicle system," India's space agency said.
The satellite had been scheduled for launch at 02:51 local time on Monday (21:21 GMT Sunday) from Sriharikota space station on India's eastern coast.
A new launch date will follow soon.
What is this mission all about?
India hopes the approximately $150m mission, Chandrayaan-2, will be the first to land on the Moon's south pole.
It will focus on the lunar surface, searching for water and minerals and measuring moonquakes, among other things.
If successful, India will become the fourth country to make a soft landing on the Moon's surface.
Only the US, China and the former Soviet Union have been able to do so.
India's Prime Minister, Narendra Modi has championed the country's space programmes, but critics would like to see poverty at home tackled first.
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The chief of the Indian Space Research Organisation (Isro), K Sivan, said this was "the most complex space mission ever to be undertaken by the agency".
If the launch had gone to plan, the lander and rover would have been expected to touch down in early September.
India's space agency is yet to give more details on why the launch was delayed and how it will affect the timeline.
India's first Moon mission - Chandrayaan-1, which launched in 2008 - resulted in the probe crash-landing on the lunar surface. But it carried out the first and most detailed search for water on the Moon using radars.
How will it get to the Moon?
Chandrayaan-2 (Moon vehicle 2) will attempt a soft landing near the little-explored south pole of the Moon.
India is using its most powerful rocket, the Geosynchronous Satellite Launch Vehicle Mark III (GSLV Mk-III), in this mission. It weighs 640 tonnes (almost 1.5 times the weight of a fully-loaded 747 jumbo jet) and at 44 metres (144ft) is as high as a 14-storey building.
The spacecraft has three distinct parts: an orbiter, a lander and a rover.
The orbiter, which weighs 2,379kg (5,244lb) and has a mission life of a year, will take images of the lunar surface, and "sniff" the tenuous atmosphere.
The lander (named Vikram, after the founder of Isro) weighs about half as much, and carries within its belly a 27kg Moon rover with instruments to analyse the lunar soil. In its 14-day life, the rover (called Pragyan - wisdom in Sanskrit) can travel up to a half a kilometre from the lander and will send data and images back to Earth for analysis.
"India can hope to get the first selfies from the lunar surface once the rover gets on its job," Dr Sivan said.
A new frontier for India's space programme
By science writer Pallava Bagla
A soft landing on another planetary body - a feat achieved by just three other countries so far - would be a huge technological achievement for Isro and India's space ambitions.
It would pave the way for future Indian missions to land on Mars and an asteroid. More importantly, it would open up the possibility of India sending astronauts to the Moon. India hopes to carry out a crewed space flight by 2022.
India also wants to assert itself as a space power to be reckoned with - and national pride is riding high as it aims to hoist its flag on the surface of the Moon.
A successful mission to the Moon would also be a win for India's ambitious space agency, which has had a string of successes recently.
In 2014, it successfully put a satellite into orbit around Mars, becoming only the fourth nation to do so. In 2017, India created history by successfully launching 104 satellites on a single mission, overtaking the previous record of 37 satellites launched by Russia in 2014.
All eyes are on Isro again. Global interest in India's frugal Moon mission is peaking, according to Simonetta Di Pippo, director of the UN office of Outer Space Affairs.
"The mission's studies of lunar topography, mineralogy, elemental abundance, the lunar exosphere, and signatures of hydroxyl and water ice will contribute to scientific progress for all of humankind," she says.
The Indian space community is nervous and Dr Sivan says "there is churning in his stomach".
"Unknown-unknowns can kill a mission, [although] no stone has been left unturned to understand all the complexities".
How long is the journey to the Moon?
The launch is only the beginning of a 384,000km (239,000-mile) journey - the robotic craft is expected to land on the Moon some 54 days later.
Isro chose a circuitous route to take advantage of the Earth's gravity, which will help slingshot the satellite towards the Moon. India does not have a rocket powerful enough to hurl Chandrayaan-2 on a direct path.
"There will be 15 terrifying minutes for scientists once the lander is released and is hurled towards the south pole of the Moon," Dr Sivan says.
He explains that those who had been controlling the spacecraft until then will have no role to play in those crucial moments. The actual landing, he adds, is an autonomous operation dependent on all systems performing as they should. Otherwise, the lander could crash into the lunar surface.
Earlier this year, Israel's first Moon mission crash-landed while attempting to touch down.
Who is on the team?
Nearly 1,000 engineers and scientists have worked on this mission. But for the first time, Isro has chosen women to lead an interplanetary expedition.
Two women are steering India's journey to the Moon. While programme director Muthaya Vanitha has nurtured Chandrayaan-2 over the years, it will be navigated by Ritu Karidhal.
"Women power is powering India's Moon ambitions," Dr Sivan said, adding that at Isro, "women and men are all equal. Only talent matters - not the gender."
Reporting by Pallava Bagla, who has written extensively on India's space programme.