By Becky Bratu and Alastair Jamieson, NBC News

(NBC) - Security cameras captured the horrific moment when a speeding train derailed on a tight curve and smashed into a wall in Spain, killing at least 77 people and injuring 178.

The dramatic footage of one of Europe's worst rail disasters, obtained by Spanish newspaper El Pais, appeared to confirm reports that the train had been going too fast as it approached the city of Santiago de Compostela late Wednesday.

U.S. citizens were among the injured, the U.S. Embassy in Spain said in a statement Thursday.

One the wrecked cars caught fire, while another slid up a grass embankment and came to rest next to a nearby road.

Images from the scene showed bodies covered in blankets and towels lying next to toppled and crushed carriages as rescuers worked to pull survivors out of broken windows.

"It was going so quickly. ... It seems that on a curve the train started to twist, and the wagons piled up one on top of the other," passenger Ricardo Montesco told Cadena Ser radio station, according to Reuters.

The driver - one of two in the cab at the time of the crash - has been put under formal investigation, a spokeswoman for Galicia's High Court told Reuters.

El Pais cited sources close to the investigation saying the driver stated immediately after the crash that he had been traveling at 118 mph on the curve, which had a speed limit of 49 mph.

Trapped in his wrecked cab, he reportedly told supervisors over the radio:  "We're human! We're human," according to El Pais. "I hope there are no fatalities because they will fall on my conscience," he said, according to the newspaper's source. NBC News was unable to immediately confirm the report.

There are reports of as many as 100 people wounded and doezens dead in a train derailment in northwestern Spain. NBC's Brian Williams reports.

All of the bodies had been removed from the wreckage by Thursday morning.

So many local residents lined up to donate blood that officials were forced to open additional donation points.

Spain's prime minister, Mariano Rajoy. declared three days of national mourning after visiting the site.

"The scene is shocking, it's Dante-esque," the head of Spain's Galicia region, Alberto Nunez Feijoo, said in a radio interview, according to Reuters.

Local health officials said 178 were injured, of which 95 were still in hospital, of whom 36 - including four children - were in a critical condition.

The crash, which happened at 8:41 p.m. local time (2:41 p.m. ET) Wednesday, was Europe's deadliest mainline train accident in more than 25 years and Spain's worst in four decades.

It also cast a shadow of tragedy over the entire Galicia region, which had been due to celebrate a public holiday Thursday.

Santiago de Compostela had been preparing for the festival of Saint James, when thousands of Christian pilgrims from around the world pack the streets. It is likely the train was packed full with people traveling for the holiday.

Officials said all of the celebrations, including a traditional High Mass at the city's centuries-old cathedral, were canceled.

The eight-car Alvia express train was traveling from the capital, Madrid, to the city of Ferrol when it derailed about two miles short of Santiago de Compostela station, national train operator Renfe said in a statement.

Spain's rail network is one of the most modern and successful in Europe, following decades of public investment.

Transport expert and author Christian Wolmar said it was not clear if high-tech safety systems, which override inputs by the driver, would have been in use at the time.

"On high speed lines, the European Train Control System should automatically correct the speed of the train, but this accident may have happened on a stretch of line which is not designated as high-speed," he said.

Rail workers' union SEMAF expressed "support for the comrade who has been implicated in this accident" as well as "condolences" to the victims, according to RTVE.

The crash is Spain's biggest disaster since the 2004 terror attack at Madrid's Atocha station that left 191 dead, and its worst train crash since 1972 when a collision left 86 dead.

In November 2000, 155 people were killed when a fire in a tunnel engulfed a funicular train packed with skiers in Austria.

In Montenegro, up to 46 people were killed and nearly 200 injured in 2006 when a packed train derailed and plunged into a ravine outside the capital, Podgorica.

NBC News' Brinley Bruton and Jason Cumming and Reuters contributed to this report.