Spark says a fault with its mobile broadband network is also having a "knock-on effect" on people trying to use their mobiles to call and text.
Spokeswoman Michelle Baguley said the fault with its mobile network, which Spark reported shortly after 11am, was intermittent.
While the mobile broadband issue had affected customers nationwide, Baguley said she believed the impact on calls and texts was "marginal".
Technicians were now resolving the problem, Baguley says shortly before 1pm.
Baguley did not believe the 84,000 Spark customers on its Wireless Broadband home broadband service had been impacted.
Spark mobile customers last experienced significant network issues in January, when a Sunday morning outage caused problems that dragged on until the evening.