Nepal floods: 'I knew I was going to die,' California couple survives deadly Himalayan disaster

• Nearly 600 people have died in the catastrophic Nepal flooding.
• Around 2,500 people are believed to be missing as rescue efforts continue.
• About 90 Americans are estimated to be among those missing.
• A California couple survived after fleeing a wall of water near the Nepal-Tibet border.
• They spent the night in a goat shed before being airlifted to safety.

A pilgrimage to Tibet turned into a fight for survival for a California couple who watched what appeared to be a dark wall of water rush towards their tour bus in Nepal.

Anjana Raja and Pattabiraman Venkatesan, from the San Francisco Bay Area, were travelling through Nepal’s Rasuwa District near the Nepal-China border when the catastrophic flooding struck.

Raja said the moment was so terrifying that she believed there was no way out.

"I knew I was going to die," Anjana Raja told CBS News. "I knew I was going to die."

The couple eventually escaped by running uphill, joining other survivors who sought refuge on higher ground. But their narrow escape came as a devastating disaster unfolded around them.

A wall of water rushed towards them

The flooding struck the mountainous border region after a glacier in the Himalayas collapsed, sending torrents of water and debris into valleys below.

The couple had been travelling by bus through Timure when they saw what Venkatesan initially thought might be a fire.

"It's like 60, 70 feet, it looked like a tsunami, but dark black," Venkatesan said. "... I could see this monster thing coming down. At that point I didn't know if it was water. I thought it was fire, forest fire, honestly."

Raja reacted immediately. She grabbed Venkatesan by the collar and pulled him away from the bus.

"Run," she told him.

They jumped from the vehicle and began racing towards higher ground as floodwaters swept through the area.

Around them, people were running for their lives. Homes and other structures were being torn apart as water and debris surged through the valleys.

"Along the way, you know, houses were coming down, it was bringing down homes," Venkatesan said.

For Raja, the human cost of the disaster was impossible to escape.

"I saw death right in front of my eyes," she said.

A desperate climb to safety

The couple followed a guide towards a flat area at the top of a nearby mountain.

The climb itself was dangerous, with mud, rocks and slippery terrain making every step difficult.

"So tall up, I don't know even how we climbed," Raja said. "It was really hard."

Venkatesan described the route as "narrow and so slippery," with "mud and stones and rocks and everything."

Eventually, they reached higher ground and found shelter in a goat shed with other survivors, including local residents and tourists.

They spent the night there before being airlifted to safety the following day.

The couple said everyone travelling on their tour bus survived.

A miracle amid a widening disaster

Their survival came as rescue teams searched through devastated communities for people who had been swept away or cut off by the flooding.

The disaster has killed nearly 600 people, while around 2,500 others are believed to be missing. The US State Department said about 90 Americans were estimated to be among those missing.

For Raja and Venkatesan, however, the numbers represent more than statistics. They saw the destruction from just feet away and experienced the terror of not knowing whether they would survive.

"The fact that we survived is nothing short of a miracle," Venkatesan said.

Now back from the disaster zone, the couple say the experience has changed how they view life.

"It strengthens my thought on life," Venkatesan said. "Be good, do good, think good, and leave the rest to whoever is above us. That's all I can say."