There were delays and cost overruns in the tunnel construction. The plan was to open it in 1993, giving the trains a head start of three years over road traffic, but train traffic started in 1997 and road traffic in 1998. During construction the sea bed gave way and one of the tunnels was flooded. The water continued to rise and reached the end at Sprogø, where it continued into the (still dry) other tunnel. The water damaged two of the four tunnel boring machines, but no workers were injured. Only by placing a clay blanket on the sea bed was it possible to dry out the tunnels. The two damaged machines were repaired and the majority of the tunnelling was undertaken from the Sprogø side. The machines on the Zealand side tunnelled through difficult ground and made little progress. A major fire on one of the Zealand machines in June 1994 stopped these drives and the tunnels were completed by the two Sprogø machines.