Pop star Demi Lovato will now perform at The O2 in two weeks' time after telling fans she was broken-hearted at being forced to cancel Sunday night's show due to illness.

The US singer was due to take to the stage in Greenwich but posted a message on Twitter telling fans she had to postpone the concert because she was ill and had swollen vocal cords.

The show has been postponed to June 25.

Lovato, 25, tweeted: "I write this through tears of frustration and sadness that I have to postpone my concert in London at the O2 tonight due to being very, very sick and with swollen vocal chords that were examined by an ENT (dr.).

"If I go on tonight and injure my vocal chords any more I could potentially have to cancel the rest of my tour.

"I'm so so so sorry to disappoint any of my fans in London that have traveled hours to be here by plane or car, and to all of the fans that got these tickets for their birthday, holiday or any other special occasion.

"It breaks my heart to let you down. Just know I feel your frustration and I wouldn't do his unless I absolutely had to.

"For everyone who bought a ticket to tonight's show, I will see you for the rescheduled date on June 25th after Madrid and Rock in Rio.

"Thank you for understanding. I love you."

The star added a broken-hearted emoji to her post.

A statement from concert producer Live Nation said: "Unfortunately due to illness, tonight's Demi Lovato show at the O2 has had to be postponed.

"The show will now take place on Monday June 25th. All tickets will remain valid for the new date.

"Please contact your point of purchase for all ticket inquiries."