NBN Co chief executive Stephen Rue says the surprise decision to spend $4.5 billion upgrading the older parts of the national broadband network to fibre was based on the sudden shift in demand brought on by the pandemic.

Speaking at The Australian Financial Review's Future Briefings on Tuesday, Mr Rue said the upgrades would be targeted first at the areas most likely to need faster services, and urged small and medium-sized businesses to take advantage of what he called a "cosmic leap in connectivity".