The order is a setback for French firm Alstom as rail competition begins to heat up on the continent.
"Eurostar International intends to order ten high-speed Velaro trains from Siemens for its London-Paris route," a statement said. "Eurostar plans to invest some €800 million in the purchase of new trains and the overhaul and refurbishment of its existing train fleet," it added.
The deal is nonetheless subject to completion of talks on final terms, said Eurostar, an international railway operator dominated by the French group SNCF.
The announcement comes as German rail operator Deutsche Bahn prepares to offer services to London for the Summer Olympics in 2012, meaning that for the first time two European railway operators will compete on a cross border route that does not connect their respective countries.
The order announced on Thursday will expand Eurostar's current fleet of 27 trains, "whose design and technology will also be overhauled starting in 2011," the statement said.
Around nine million passengers take the train each year on the Eurostar routes between Brussels, London and Paris.
Deutsche Bahn is to make a much-awaited test run to London on October 19, but Eurostar boss Nicolas Petrovic was quoted as saying the new and renovated trains would "bolster our position as the dominant rail operator between the United Kingdom and the continent."
The Velaro train is one of Siemens' flagship products, and can carry up to 900 passengers, or 20 percent more than trains now in circulation, at 320 kilometres per hour.
It would connect London and Paris in just over two hours, London and Amsterdam in less than four hours, and London and Geneva in about five hours.
Siemens has already sold the trains to railways in China, Russia and Spain, but lost out to Alstom's AGV train in an Italian tender.
A third major rival in the market for high-speed trains is the Canadian group Bombardier, and all pitch their products as environmentally friendly transportation options.
The statement said the Siemens trains, which run on electricity, consumed the equivalent of 0.33 litres of petrol per passenger per 100 kilometres, or "just enough to fill a can of coke."
France and Britain have fixed conditions for trains that wish to use the Channel tunnel, in particular their length, that are only met by Eurostar trains that now connect London with Brussels and Paris.
That effectively blocks rivals to Eurostar, owned by France's state-owned rival SNCF, its Belgian counterpart SNCB and the British group London and Continental Railways. A working group has been established to review the situation, however, and Eurotunnel has called for rival railways to come forward, suggesting the possibility of offering services between London and Amsterdam or Frankfurt.