The driver, who is thought to have retreated in his cab moments before the crash, is being treated in hospital after suffering serious injuries.
Rail workers in southern Belgium went on strike in reaction to the crash.
Train links have been widely disrupted. The Eurostar to and from Brussels has been suspended for three days.
An investigation into the cause of Monday morning's train collision is under way, amid suggestions that one train may have driven through a red signal.
Investigators are looking at whether human error, mechanical failures, or the weather may have been primarily to blame.
They have recovered two data recorders, or "black boxes", from the trains which they are now due to examine, Belgian media reported.
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