Police and recovery teams are preparing to remove the wreckage of the concrete mixer which fell from a bridge onto a train at Oxshott, Surrey.
The 26-tonne vehicle crashed through a brick wall onto the Guildford to Waterloo train which was passing below.
Five of the 40 passengers travelling on the eight carriage train were injured, two seriously.
The 38-year-old lorry driver was freed from the wreckage and taken to hospital.
"His injuries don't appear to be as serious as first thought and are not life-threatening," a hospital spokesman said.
The incident happened at about 1530 GMT on Friday on Warren Road, a short distance from Oxshott railway station.
The vehicle struck the third carriage from the back of the train punching a large hole in the metal roof.
The Conservative MP for Esher and Walton, Dominic Raab, has been at the scene of the incident.
Mr Raab said: "We will have all the inquiries and forensics conducted in the days and hours ahead, both by the police and also by the rail accident investigation branch.
Return to normal
"But we will have to wait for the outcome as to why this happened and to make sure it doesn't happen again."
It may be Monday before rail services in the area can return to normal.
The injured passengers were taken to various hospitals following the accident.
A 60-year-old passenger was taken to St George's Hospital as a "precaution". The other injured passengers were treated at Epsom General Hospital in Surrey and the Royal Surrey County Hospital.
Passenger Ade Joshua told BBC News: "In the carriage right next to us where the incident happened, there was a guy trapped with what looked like a broken back, so we were trying to console him as much as we could until the emergency services arrived.
"But we couldn't actually get through to the carriage because the door was blocked as that bit of the train collapsed."
Timi Raji, 18, who was in the carriage next to the one that was crushed, rushed to the adjoining door when the train ground to a halt following a loud bang.
He said: "The door was blocked but we could see someone was at the bottom of the carriage, trying to get out.
"The train had been crushed and the guy was trying to escape.
"He was on his stomach and we could only see his feet sticking out. My friends and I were trying to calm him down and talking to him."
Witness Nikki Karim works in a taxi office near to the crash site.
She said: "There's a lot of police at the station, there's a few minor casualties that are sat at the platform."
She added: "You don't expect this sort of thing to happen."
The incident took place on a branch line, and is unlikely to result in major disruption.
The bridge from which a lorry fell was assessed as safe in the nationwide checks made after the Selby rail disaster nearly 10 years ago.
The checks were ordered after a Land Rover came off the road and on to the East Coast Main Line in February 2001.