GEOFF BENNETT: Welcome to the "News Hour."

Three days after a catastrophic wall of water, mud, and rock tore through Nepal's Himalayan valleys, the scale of the disaster is still coming into focus.

Nepalese authorities say at least 579 people are now confirmed dead, and nearly 2,000 remain missing.

The casualty situation in China is not yet clear.

AMNA NAWAZ: And, tonight, the danger is not over.

Authorities are closely watching lakes formed in the wake of that glacier collapse amid fears of further flooding.

Stephanie Sy begins our coverage.

STEPHANIE SY: In Nepal, the violent floods that raged through these valleys two days ago left haunting reminders, the banks of the Trishuli River now awash in gray mud, within these communities, cries of grief and trauma and warnings of more danger.

Police officers rode through the streets today shouting, "Stay away from the river," as residents, still shaken, ran to higher ground.

Officials are monitoring a number of lakes formed by landslides overflowing.

Crammed with debris, they present a high risk of more flooding.

INDIRA ADHIKARI, Evacuated Resident (through translator): The flood is causing huge problems for us.

Our house is now full of mud.

We are young and still facing so much trouble walking and evacuating.

Imagine how tough it is for old people in such a situation.

SURAJ SIGDEL, Mercy Corps: I have seen so many disasters, but this one, with the level of devastation, it's very difficult for me.

STEPHANIE SY: Suraj Sigdel is the Nepal country director for the aid organization Mercy Corps.

He told the "News Hour" search operations were paused today after the new flood alerts went out.

SURAJ SIGDEL: My team was supposed to go to the ground zero this morning, and we were cautious about more flooding.

And the lake is being formed at the Tibetan side of the border, and which might overflow or burst any time.

We are in the monsoon season, so, like, the erratic rain is always expected, so it can rain anywhere, and it will have devastating impact if it rains heavily or the cloud burst in the flood-affected areas.

STEPHANIE SY: The dramatic images that have emerged from Wednesday's disaster speak for themselves, the river transformed from calm to crushing within seconds.

Construction workers at this hydroelectric dam ran for their lives as the wave of water and earth accelerated toward them.

MAN: Oh, my God.

Oh, my God.

STEPHANIE SY: Nepal's army says it has pulled 350 people to safety from this tunnel running underneath a hydropower plant.

Officials believe more than 100 people are still trapped inside.

China state broadcaster showed Premier Li Qiang today visiting the flood zone in Tibet, where emergency crews have relied on inflatable rafts.

Nepal's army has used helicopters to pluck people from their rooftops.

Despite offers from international rescue teams, Nepalese officials say their in-country rescuers are sufficient for now.

SURAJ SIGDEL: Nepal's army is equipped, and they have the capacity to do so.

And they don't want to, like, bring in many international people and then risk the coordination for it.

So that is the logic of government.

STEPHANIE SY: But other aid may be coming, emergency supplies from the U.N., as well as India, and financial pledges from South Korea and the U.K.

The U.S.

State Department says it is sending Nepal $500,000 in assistance.

The Red Cross says more than $30 million is needed for its response.

Based on satellite imagery and on-the-ground data, scientists now believe the bedrock underneath the Himalayan glacier collapsed.

The massive rock fell more than half-a-mile down, shattering debris into the valley's rivers, which surged with deadly force into villages.

Experts say climate change, if not a sole cause, may contribute to such phenomena.

Sigdel said he had no doubt.

SURAJ SIGDEL: We consider it as a climate-induced disaster.

We are disappropriately impacted by this climate change, and we are being punished for something that we have not done.

So, yes, we feel like it's not a justice.

STEPHANIE SY: As the casualties mount, stories of survival have surfaced as well.

Maddie Tamong (ph) thought for sure she was facing the greatest loss of her life.

MADDIE TAMONG, Mother (through translator): I had come to accept that both my children were gone.

I went through the jungle full of leeches, crossed rivers, weeping and frantically searching for them.

At last I have found both my children.

They were injured, covered in scratches, but I found them.

STEPHANIE SY: She was reunited with them, scratches and all.

For the "PBS News Hour," I'm Stephanie Sy.