Netflix has unveiled a warning trailer about its controversial series 13 Reasons Why ahead of its second series.

In the video, cast members say the show "may not be right" for people struggling with issues such as sexual assault, suicide or substance abuse.

It comes after mental health groups were among those to have raised concerns about how the show depicted suicide in the first series.

The show tells the story of a US high school student who takes her own life.

In the video, Katherine Langford, who plays Hannah Baker - the student who kills herself - says: "By shedding a light on these difficult topics, we hope our show can help our viewers start a conversation."

Alisha Boe, who plays Jessica Davis, adds: "But if you are struggling with these issues yourself this series may not be right for you."

Dylan Minnette, who stars as Clay Jensen, tells viewers if they feel they need someone to talk with they should "reach out to a parent, friend, school counsellor or an adult you trust".

The trailer will autoplay before the first episode of each series on Netflix.

13 Reasons Why has been praised for raising awareness of the problems teenagers can face, including sexual assault and mental health.

But it has also generated controversy for showing the suicide of the central character, Hannah, in detail.

Following the success of series one, Neflix commissioned research which it says found that "nearly three-quarters of teen and young adult viewers said the show made them feel more comfortable processing tough topics".

However, the study also found that parents felt that they wanted more resources from Netflix.

As a result, it's introduced a discussion guide and contact numbers of mental health organisations to the show's official website.

Brian Wright, vice president of original series at Neflix, said: "The hope is that the steps we're taking now will help support more meaningful conversations as season two rolls out later this year."