Rita Ora has apologised to fans as she announced she would not be performing at a music festival after spending the night in hospital.

The music event in Hungary also confirmed her concert was cancelled "due to illness".

The British singer-songwriter, 33, did not reveal details of her health but said she "must rest thoroughly and follow doctor's orders".

She said in an Instagram Story message to her 16 million followers that she would not be performing at Campus Fesztival in Debrecen, Hungary, on Saturday evening.

The Kosovo-born star also revealed she had spent the previous night in a Budapest hospital.

Ora shared the statement just hours before she was due to sing in Debrecen.

She said she was "so sorry" to fans who were going to be at the event and "I'm truly thankful for your understanding".

The festival has issued a post on Instagram about the situation.

Organisers shared Ora's statement and wrote in the caption, translated into English: "[Her] crew has been working since dawn to set up the show... we are devastated by the news too.

"Saturday's programme of the main stage will be reorganised soon. We wish Rita a speedy recovery."

A statement on the festival website said: "Rita Ora arrived in Hungary two days ago, but today's concert in Debrecen will be cancelled due to illness.

"[Her] crew has been working since dawn on the preparation of the show... we were also devastated by the news."