Hermann Tilke, the renowned F1 circuit architect, is in charge of the layout for the new project in Rio de Janeiro.
Strongly backed by new Brazilian president Jair Bolsonaro, a new track named after Ayrton Senna looks set to replace Interlagos as the 2021 Brazil GP host.
However, Interlagos - in Sao Paulo - is not yet giving up, insisting its 2020 contract with F1 be honoured.
"There is no doubt that we have what it takes to continue hosting the Brazilian GP, both from the organisational and security point of view," said Sao Paulo mayor Bruno Covas.
"As we wait to know our future, we will continue with our usual work," he added.
But Globo reports that the Rio project has taken another big step forward, with construction getting official approval to go ahead from city officials on Monday.
"Today's achievement is the completion of a process we began more than four years ago," said the Rio promoter, JR Pereira.
"We have put together the best in the world in terms of technical capacity to guarantee Rio de Janeiro a race track for the most modern motor sports in the world," he added.
Tilke, who was the track designer in charge of most of the modern circuits on the calendar, said: "The proposal we have brought to Rio is for the design of a modern circuit that is dynamic and full of emotion."
