The Rail, Maritime and Transport (RMT) union has said a major incident was narrowly avoided after a commuter train nearly crashed into debris on the tracks near Liverpool Lime Street Station.
Rubble was strewn across tracks between Liverpool's major train station - through which roughly 15 million people travel each year - and Edge Hill after a wall collapsed on Tuesday evening.
The RMT claims "at least" one train was merely seconds away from colliding with the debris shortly after the collapse.
Commuters were left stuck on trains which were forced to halt while emergency services worked to clear the rubble, but it effectively cut off the station from the rest of the network, creating disruption for thousands of people.
Normal services only began to resume on Thursday. The RMT's general secretary, Mick Cash, praised the quick response by railway staff and the emergency services, saying it was lucky the incident didn't become a major disaster.
He added that the incident demonstrates the folly of plans for driver-only trains, which are reportedly being considered by Arriva Rail North, the major train operator in northern England. The plans have already brought months of strike action on the Southern Rail network, led by RMT - which represents train guards.
Cash said: "Without guards to keep passengers calm and lead safe evacuations, we might have had the potentially lethal prospect of passengers de-training themselves in dark tunnels or stumbling towards tons of debris and damaged power lines."