A ship carrying 2,400 tons of sulfuric acid capsized on the Rhine River in Germany early Thursday, causing two crews missing and a halt on vessel traffic, authorities said.

The ship overturned on the river near the famed Loreley Cliff, about 30 km south of the German tourism city Koblenz, German Federal Shipping Administration said in a statement.

Two crew members were rescued, taken to hospital and in good condition, while the other two were still missing, waterway police said.

The authorities have suspended all shipping traffic on the Rhine, one of the busiest waterway in Europe. A helicopter with thermal imaging cameras was sent to help find the missing.

The 100-meter-long vessel carrying 2,400 tons of sulfuric acid was sailing from Ludwigshafen in southwestern Germany to Antwerp, Belgium, the authorities said.

Waterway police said they were trying to secure the tank and that no acid leaking had been discovered in the flow as of Thursday morning. However, the area of accident has treacherous currents.

The cause of the accident was not immediately known.