Five Eurostar trains were cancelled and others delayed following a power failure which left hundreds of passengers without any air conditioning.
Up to 700 passengers had to be taken from their train after temperatures inside the carriages rose to more than 40C.
The high-speed Brussels to London train stopped near Halle in Belgium, before they were led off and waited at the side of the track.
A train arrived three hours later to take passengers back to the Belgian capital.
Eurostar said the train doors were opened for ventilation and staff handed out water.
It is the second time Eurostar has been hit with a power problem this month.
Last week services were delayed after power failed near Lille.
More: Eurostar dismisses reports of no-deal Brexit chaos [Feb 19]
Eurostar highlights green credentials with extra Amsterdam frequency [June 19]
