More than 100 people have complained they couldn't hear what characters were saying during last night's first episode of Jamaica Inn.

The BBC says there were "issues with the sound levels" on its new period drama. Members of the show's crew also indicated that the muffled sound was not intentional, including writer Emma Frost:

No surprises here - I'm told there was a major sound problem for tonight's broadcast of #JamaicaInn - not surprised you couldn't hear it

— Emma Frost (@EmmaFrostLondon) April 21, 2014

Despite the issues, over 6 million people are estimated to have tuned in to watch the drama, which is an adaptation of Daphne du Maurier's novel.

Bosses say a review is underway before the second episode is shown tonight, with the third and final episode due to broadcast on Wednesday.

Jamaica Inn stars Jessica Brown Findlay, Shirley Henderson, Sean Harris and Joanne Whalley.