London, England (CNN) -- Twenty-one people were injured when a train crashed into a sewage tanker in the town of Sudbury in England, police said Wednesday.
The National Express East Anglia train was traveling between Sudbury and Marks Tey on Tuesday evening when it hit the tanker at an unmanned level crossing, the British Transit Police said.
A 58-year-old man suffered life-threatening injuries and was in serious but stable condition Wednesday morning, police said.
Six more people stayed overnight at a hospital with injuries including broken ribs, back and chest pain, and heavy bruising, police said.
The train driver was among the injured.
Police planned to bring in a 130-ton crane to the site later Wednesday as part of the recovery operation.
The train was carrying 20 passengers when the collision happened, police said. It remained upright, but the first carriage derailed, police said.
Suffolk Police arrested a 38-year-old man from Cambridgeshire on suspicion of dangerous driving following the collision, and the tanker was removed from the line shortly after midnight.
An investigation to determine the cause of the crash is under way.
CNN's Laura Perez Maestro contributed to this report.