Eurostar, the company that runs trains between London, Paris and Brussels, said it had suspended all trains in and out of Britain on Saturday due to a trespasser on the line.
"We have suspend all services to and from London St Pancras this morning, due to a trespasser on the tracks," Eurostar said, urging passengers not to travel on Saturday morning.
A Eurostar spokeswoman said the trespasser was located near St Pancras station and all services were suspended until at least 0945 GMT.