NEW YORK/DUBAI: Some were on their honeymoon, others were studying abroad, many were building new lives in foreign countries. But when Israel called up its reservists and declared war this week, the response was swift and overwhelming.

"Everyone is coming. No one is saying no," said Yonatan Steiner, 24, who flew back from New York, where he works for a tech company, to join his old army medical unit.

"This is different, this is unprecedented, the rules have changed," he said, speaking by phone from the border near Lebanon where his regiment is based.

Israel has called up 360,000 reservists in the wake of Saturday's assault by hundreds of Hamas gunmen who overran towns, kibbutzes and army bases near the Gaza enclave, killing more than 1,200 civilians and soldiers and wounding over 2,700.

Most reservists were already in Israel at the time of the call-up - the largest such compulsory mobilisation since the 1973 Yom Kippur War. But many were out of the country, for a variety of reasons, and dropped everything to rush back.

Nimrod Nedan, a 23-year-old studying medicine in Lithuania, said friends and relatives died or were missing as a result of the surprise Hamas attack, spurring him to action.

"I cannot sit here and study medicine while I know that my friends are fighting and my family needs protection. This is my time," he said.

L.K. - a 37-year-old reservist who served as an air force pilot for 13 years, and asked to be identified just by his initials for security reasons - felt exactly the same.

He works for a tech company in New York, and left his home, wife and children to hurry back to his squadron. "There is no other place in the world I would rather be. If I had to sit in my lovely apartment on the Upper West Side watching this I would never forgive myself," he said.

FINDING TICKETS

Military service is compulsory for the majority of Israelis when they turn 18. Men have to serve 32 months and women 24. After this, most of them can be called up to reserve units until the age of 40, or even older, in case of national emergency.

In times of war, they fight alongside the regular troops.

Yonatan Bunzel only finished his military service this year, making him exempt from immediate reserve duties, and like many Israelis just out of the army, he went travelling to celebrate his demobilisation.

He was in India when Hamas struck and despite not being obliged to return, Bunzel nonetheless packed his bags and headed home, five months ahead of schedule.

"My immediate reaction, of course, was shock and I didn't know exactly what to do. But after a few hours, my mind had cleared and I just knew I had to go back home, save my country, help my people, give my part," he said.

Reaching Tel Aviv was easier said than done. After flying to Dubai, Bunzel found there were no tickets available for Israel. However, a Jewish non-profit organisation, La'aretz, stepped in and secured seats for him and two of his friends.

Other Israelis recounted how their local consulates had provided free trips home, while U.S. media reported that people were going to the counters of Israeli airline El Al in New York and offering to buy tickets for anyone with call-up papers.

While many foreign carriers have cancelled flights to Tel Aviv, Israeli airlines have added flights on foreign routes to bring people back, while the military dispatched transport planes to some European cities to collect soldiers.

LIVES UP-ENDED

Israelis abroad are using WhatsApp chats to organise their return, sharing information on where to find available flights, said Yedidya Shalman, 26, who was in Thailand on his honeymoon when the violence exploded out of Gaza.

"(We) set up WhatsApp groups almost everywhere in the world, we called people to join them and we slowly worked to bring as many reservists as possible back to Israel," he said, explaining that he and his wife did not hesitate to curtail their holiday.

"Of course we didn't think twice and are currently on our way home on an El Al plane," he said via WhatsApp.

The mass mobilisation has not only wrecked holidays but also up-ended lives.

Oren Saar, 37, runs a food delivery startup, WoodSpoon, in New York City, where he lives with his wife and three young boys. A former captain in the Israeli army, he immediately acknowledged the call-up, but didn't tell his children what he was doing.

"The kids are very young and it's not really something that you want to explain. We told them I'm going on a business trip to Israel," he said, adding that it was going to be "tricky" to keep his new business going in his absence.

"But you know, there's just no question about what to do when my friends, my family and my country are at risk," he said.