A sprawling garden of radishes, carrots and rhubarb is flourishing at the top of the 150m tall Bank of America tower, a stark and colourful contrast to the monotone shades of concrete, steel and glass of the city's financial district.

The farm is among more than 60 that have sprouted across the space-starved city since 2015 - on decommissioned helipads, shopping mall rooftops and public terraces - thanks to initiatives like Rooftop Republic, a local social enterprise which promotes urban farming.