Former Formula 1 boss Bernie Ecclestone has warned against the move towards more street circuits on the calendar, something Liberty Media is seemingly pursuing.

The current bosses have already confirmed a new race in Vietnam for 2020 on the streets of Hanoi and are also considering a London race if a new deal with Silverstone can't be reached for the British Grand Prix.

Copenhagen was another city weighing up the possibility but it's Miami and the proposed event there in two years time that Ecclestone focused his comments on.

"We have to be careful with these street circuits," he told Speed Week. "Tracks like Monaco or Baku, these are true street circuits but if you invent roads to get a road race, that's not the same thing.

"[In Miami] they wanted to drive on an island, over a bridge, such things, very difficult to implement."

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The Briton has long doubted whether the Miami Grand Prix will ever get off the ground, having attempted a similar plan in New Jersey which fell through earlier in the decade, and claims the Floridian city was another non-starter during his tenure.

"I shot Miami down a long time ago, it will never happen," Ecclestone believes. "I think that whoever wants to host a race in America wants a guarantee not to lose money.

"They're in too much of a hurry with all these new races. When they showed up, they said 'we'll have 25 races, six of them in America.'

"But when they come up with their business plan, they sit down and write down what they want to happen. However, they do not know how to do it and that's exactly the problem."