The zero-carbon city that Saudi Arabia plans to build at Neom will vertically layer homes, offices, public parks and schools within a mirrored facade stretching over 170km, the crown prince said in remarks carried by state media.

Crown Prince Mohammed bin Salman first announced plans for "The Line" in January 2021.

It is the first major construction project for the $500bn Neom business zone aimed at diversifying the economy of the world's top oil exporter.

The city, 200 metres wide and running on "100% renewable energy," will also include a high-speed rail with an end-to-end transit of 20 minutes.

It will eventually accommodate 9m residents, state news agency SPA cited him as saying.

"The city's vertically layered communities will challenge the traditional flat, horizontal cities," the prince said.

"The designs of The Line embody how urban communities will be in the future in an environment free from roads, cars and emissions."

The prince had said last year that the project's infrastructure would cost $100bn to $200bn.

SPA did not provide any updated figures.

The kingdom's sovereign wealth fund, the Public Investment Fund, is the cornerstone investor in Neom.

The 26, high-tech development on the Red Sea will have several zones, including an industrial and logistics areas, planned for completion in 2025.