Vocus Communications chief executive Geoff Horth has warned that fast-developing 5G wireless technology could pose a significant threat to the uptake of services on the National Broadband Network.

This would leave the NBN seller with a smaller market to operate within, Mr Horth said as he unveiled reduced profit guidance for the year at the company's interim result announcement.

Vocus Communications chief executive Geoff Horth has flagged concerns about the future of the NBN. Credit:James Alcock

Mr Horth said there was "talk" in the industry of 30 per cent of households opting for wireless networks in the future, compared to original assumptions that only 15 per cent would opt out of a fixed broadband connection.

Vocus is particularly affected by the uptake of NBN services as it is a wholesaler of broadband to smaller telecommunications companies. Investors reacted sharply to the news sending Vocus shares down 10.11 per cent to $2.58 by market close.