Cancelled flights, missed connections and expiring visas have turned Bali into a nightmare for thousands of tourists scrambling to leave, as a volcano on the Indonesian vacation paradise threatens a major eruption.

Hundreds of flights have been grounded as the main international airport was shuttered for a second day on Tuesday, leaving 120,000 stranded visitors in need of shelter -- or an exit plan.

Hundreds joined the mad rush to board buses headed to an international airport in Indonesia's second-biggest city Surabaya -- 13 hours' drive and a ferry ride away -- as torrential rains dampened spirits even more in one the world's top tourist draws.

The imminent eruption of Mount Agung may mean more five-star hotel living for some well-heeled visitors who are happy to sit out the minor inconvenience, but Mukesh Kumar Gupta and two-dozen members of his family aren't going to be staying at the Four Seasons.

"We are practically helpless -- how can we get back to India?" said the Chennai-based member of the heaving 26-member clan.

Gupta's family -- 23 adults and three kids -- arrived in Bali 10 days ago from different Indian cities.

They were all supposed to fly back Tuesday but now they say they are stuck, and nearly broke, as chaos ensued at the airport with frustrated travellers and overwhelmed staff.

"The refund money (from the airline) won't be enough to buy us new tickets," another family member, Navin Saraf from Kolkata, told AFP at Bali's main airport.

"We booked everything online beforehand, so we don't have much cash right now," he added.

Towering columns of thick grey smoke have been rising from Agung since last week, and in the last few days the volcano has begun shooting smoke and ash into the sky, forcing all flights to be grounded until at least Wednesday morning.

Ash is dangerous for planes as it makes runways slippery and can be sucked into their engines.

- 'Nobody's fault'-

Agung is 75 kilometres (47 miles) from the beach-and-sandal tourist hub of Kuta, but that wasn't making German student Alex Thamm feel much better.

"We are supposed to go back to Germany via Singapore on (Friday) but the situation seems not good," he said nervously.

"Is it dangerous here? Do you think [the volcano] will explode?"

The delays weren't putting a smile on Juan Gajun's face either, after he missed a connecting flight Monday.

"We have to leave the island and we can't. We were planning to go to Singapore but we have to stay here for I don't know, maybe two or three days more," said the 30-year-old Argentine.

Colin Cavy, a French dive master who has been in Indonesia for a couple of months, had other problems.

"I've just come to Bali two days ago to leave the country," he told AFP.

"My visa has expired...I need to go to the immigration office."

Meanwhile, cash-strapped Gupta and his bulging brood were weighing their options, which he lamented would not include help from India's consulate in Bali.

"No one can beat nature, but at least people can help," said Gupta's relative Abhisek Garg, who lives in Delhi.

They might want to call inn operator I Wayan Yastina Joni, who is among the few hoteliers willing to take up an appeal by Bali's governor and tourism agency to supply free rooms to out-of-luck visitors.

"I don't mind giving free accommodation for tourists I already know," said the owner of the Pondok Denayu Homestay.

"This is nobody's fault. It's a natural disaster that no one expected."