Eurostar has started a rail shuttle service between London and Brussels.
Three trains a day will run the route from today (February 22), although a diversion around the crash site means the journey takes an extra 50 minutes.
From Friday the capacity on the route is likely to be expanded, but continue on the diverted route.
Eurostar said: "The new route is on suburban commuter lines and access is severely restricted, therefore Eurostar is only able to operate three return trains rather than the usual nine services in each direction."
The direct train services will continue to be reinforced by the shuttle coach service between Lille and Brussels.
Full services between London and Brussels are not expected to resume until Tuesday March 2 "at the earliest", added Eurostar.
Passengers who decide not to travel can exchange their tickets for travel on a later date or get a refund.
Services to Lille have also been increased today, but Eurostar warned there may be some delays.
Passengers travelling to Lille or Brussels have been told to check-in as normal "and they will be accommodated on to most appropriate service".
Eurostar services to Paris have also seen delays this morning, after passengers on last night's 8.43pm train from Paris were left stranded in Kent for more than an hour due to a technical problem.
The travellers had to board a rescue train after the Eurostar train lost all power, reports say.
Eurostar said, in a statement on its website: "Due to operational restrictions in the South Kent area, some Eurostar services may be delayed by up to 60 minutes this morning."
www.eurostar.com