Fundamental Architects and Omega Render have envisioned a building spanning a river in Nursultan, capital of Kazakhstan, with a hole in the middle to make it look like the national flag.

Rotterdam-based Fundamental Architects and visualisation studio Omega Render produced the design for BI Group, Kazakhstan's largest developer.

Named Tower of the Sun, it is one of three designs that the developer is considering for the site in Nursultan, the city formerly known as Astana.

The 75,000 square-metre-building is proposed for a site near the Ak Orda Presidential Palace in the centre of the city. It would be built across the Ishim river, with the lower level becoming a public pedestrian and cyclist bridge.

A large hole, which is designed to represent the sun in the Kazakhstan flag, would be cut from the centre of the 121-metre-tall block.

"The building shape took its inspiration from the national flag of Kazakhstan – a blue rectangular canvas with a yellow circle in the centre," said Vladimir Konovalov of Fundamental Architects.

The hole in the middle would also serve a function – it would maintain views of the palace from the nearby highway.

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"The building is strategically positioned on the view line between the main highway and the palace, so while driving on a highway we do not block the view towards the Presidential Palace," Konovalov told Dezeen.

"It is still visible though a circle opening in the tower, which represents a sun – an important symbol in Kazakh culture and traditions," he said.

Above the public bridge, the building would contain a two-storey-high shopping mall, with luxury flats and offices on the floors above. The building would be topped by a publicly accessible roof terrace, which would offer views across Nursultan.

"It becomes an important attractor on the city scale and provides a much needed pedestrian connection between two important landscape parks that are positioned on different sides of the river," added Konovalov.

Fundamental Architects and Omega Render have designed the building to have "near net-zero energy requirements". As part of the plan, the river running under the building would be narrowed to increase its flow so that it can be used to generate hydroelectric power.

Astana was renamed Nursultan in March 2019. The city hosted a world expo in 2017. At the time, architectural photographer Paul Raftery captured some of the city's "crazy array of architecture".