Twenty-three people died and 10 were injured when an elevated magnetic train ploughed into a maintenance vehicle in north-western Germany.
Rescuers had to use ladders and cranes to reach the train
The train, which floats on a monorail via a magnetic levitation system called maglev, was going at nearly 200km/h (120 mph) when it crashed near Lathen.
Damaged carriages were left balancing on track 5m (16ft) in the air, hampering rescue efforts.
"Today we are in mourning," said Chancellor Angela Merkel at the scene.
The accident happened at about 1000 (0800 GMT), on a 31.8km (20 miles) test track from Lathen to Doerpenwhich is used for tourist trips and to demonstrate the technology.
Emergency workers used fire ladders and cranes to reach the carriages. Several metres below, the ground was strewn with wreckage.
Reports said up to 30 passengers on the train - mostly employees working on the system and staff from a local utility company, RWE.
The maintenance vehicle hit by the train had two crew members.
A spokesman for IABG, the company which operates the train, said the accident had been caused by human error, rather than a technical fault.
Ms Merkel arrived by helicopter near the scene. Dressed in black, she extended condolences to the victims and their families: "I want to show that I am with them," she said.
The Transrapid system, run by Siemens, is capable of speeds of up to 450km/h (280mph).
The only commercial example of a Transrapid system in operation is the high-speed shuttle to China's Shanghai airport from the city centre.
It was developed by Transrapid International, a joint venture between Siemens AG and ThyssenKrupp.
German Transport Minister Wolfgang Tiefensee, who is in China, has cancelled his trip and is now on his way back to Germany.
In August, a fire broke out on a Transrapid train in Shanghai, adding to concerns about the safety of the technology.
The German companies are keen to make Transrapid an export hit and negotiations are under way about building another link in China, and also in Munich, the BBC's Tristana Moore reports from Berlin.
HOW MAGLEV TRAINS WORK
Like poles on magnets keep train above track
Train is propelled by electro-magnetic system in the sides of the "guideway" instead of onboard engine
Top speed (with passengers) - 450km/h (280mph)
Developed by Transrapid Int in Germany
Operating commercially in Shanghai
Test facility in Emsland, northern Germany, is longest of its kind at 31.5km (19.5 miles)
Source: Transrapid International
Do you live in the area near the crash scene? Did you witness the accident? Send us your comments using the form at the bottom of the page:
If you have pictures or moving footage you can send them to firstname.lastname@example.org or text them to 0044 7725 100 100. You should not endanger yourself or others, take any unnecessary risks or infringe any laws.
Here are a selection of comments received so far:
Having used the Maglev train in Shanghai, this should not be used as an excuse to delay further development of this fantastic, environmentally friendly piece of technology. It's apparent that the train hit a maintenence vehicle, thus human error is 100% responsible. This train could offer London - Brighton services in 7 minutes, and further development should continue.Sam, London, UK
What an absolutely tragic and mournful day this has been. Although I'm living several kilometers away from the crash scene, this massive extent of devastation is so gruesome and frightening. It's just unbelievable how human failure can cause so many fatalities so quickly.Martin, Neuss, Germany
I recently rode the Mag Lev train in Shanghai. I've travelled many forms of transit from the underground to Concorde. I came off my round trip feeling very ill at ease - and I remember saying to my friend that if something were on the track at these speeds we would be finished (which is one reason the tracks are elevated). The feeling is very different from the Japan bullet trains or the French TGV. My heart goes out to the family and friends of those killed and injured.David, Santa Monica, USA
I was in the cab of the Transrapid train during a high-speed run at the test track in Lathen on August 18 in connection with my work as a transport journalist. They showed me some of the maintenance vehicles and I can only imagine it would have been a terrible crash if the train hit one of them at speed. It strikes me that the accident does show a weakness in the technology. If a maintenance train were left on the track on a normal railway, it would be impossible to turn the signal behind it to green. There clearly wasn't any such system at Lathen. Robert, London, UK
The BBC may edit your comments and cannot guarantee that all emails will be published.