The crash, near the Sinai Desert border to the north of the Red Sea resort of Eilat, was the worst in Israel for years.
Israel’s ambulance service reported 24 dead, many of whom were Russian. The Russian ambassador to Israel, Pyotr Stegniy, told Moscow’s state-controlled Vesti-24 channel that the latest figures he had from Israeli authorities stated that 30 people were killed and 21 were injured.
There was no immediate Israeli confirmation of the higher death toll.
Soldiers, police and rescue workers rushed to the scene and army helicopters flew in to evacuate survivors, who had just arrived in Israel.
“I saw people flying out of the windows as the bus rolled down the slope,” said one taxi driver who witnessed the crash.
Bodies, baggage and wreckage were scattered down the steep slope beneath a winding highway, according to witnesses at the scene, where the tour bus lay on its side on the desert floor of a rocky canyon.
An Israeli officer shouted instructions through a bull-horn as stretcher teams laid out a line of white plastic body-bags.
Army helicopters shuttled to and from the crash scene beyond nightfall, ferrying the worst of the injured to a hospital in Beersheba. Ambulances raced others into Eilat for treatment.
“Suddenly the bus started to fall off the left side and from there I don’t remember a thing. I woke up lying on the ground,” Yelena Potyomkina, a 56-year-old passenger, told Israel’s YNET news website.
Israel’s Tourism Ministry said the bus was one of two carrying a group of travel agents who had just arrived from St. Petersburg at nearby Ovda airport, which serves Eilat.
The Red Sea resort on the Gulf of Aqaba, at Israel’s southern tip bordering Jordan and Egypt, is a popular destination for northern tourists seeking winter sunshine.
Russian authorities said they were sending two planes to Israel with relatives and specialist medical personnel.
“Tonight we plan to dispatch two emergency ministry aircraft to Israel. One plane will fly from Moscow to St Petersburg and then Eilat bringing relatives of those who suffered in the crash,” a spokeswoman for the Emergencies Ministry said.
“A cargo plane will head for Eilat as well. It will carry medical staff, psychologists, rescue workers and necessary medical equipment.”
Police spokesman Micky Rosenfeld said an initial police investigation was focusing on whether the bus driver lost control while trying to overtake another vehicle.