Viacom has reported weaker-than-expected quarterly revenue, hurt by lower advertising revenue from its US cable TV business as viewers increasingly shift to online streaming services.

The results add to investor concerns over the US cable industry after disappointing numbers from Walt Disney, Twenty-First Century Fox, Discovery Communications and Time Warner this week.

Viacom's shares plunged as much as 18% to a near four-year low yesterday. 

Shares of Disney, Fox, Discovery and Time Warner also fell for the second straight day.

Concerns over viewers cutting the cord on cable TV and moving online increased on Tuesday when Disney lowered its profit forecast for its cable business.

Viacom's advertising revenue fell 9% in its US cable business, the fourth straight quarter of decline.

The company has been hurt by lower Nielsen ratings for some of its shows. Nielsen ratings, based on feedback from viewers, have long been the metric advertisers use to negotiate TV ad rates and make their decisions.

Viacom says that Nielsen ratings do not adequately reflect its viewership as viewers are shifting to digital platforms such as tablets and smartphones for their entertainment fix.

Revenue from Viacom's movie studio business, which includes Paramount Pictures Corp, fell 44% to $479 million. The company had benefited in the year-earlier quarter from the release of its blockbuster ‘Transformers: Age of Extinction’.

Viacom's movie slate for the fourth quarter includes ‘Terminator: Genisys’ and ‘Mission: Impossible - Rogue Nation’, which are expected to drive revenue.

Net profit from continuing operations attributable to Viacom fell 3.3% to $591 million, or $1.47 per share, in the third quarter ended 30 June.

Excluding items, Viacom earned $1.47 per share.

Revenue fell 10.6% to $3.06 billion.