NEW YORK • Ariana Grande is ill, but what is most sickening for the singer is that she is "not really sure what is going on".

On Sunday, Grande, who is on a world tour, had to cancel her concert in Lexington, Kentucky.

"I woke up kind of 10 times worse and it hurts so bad to swallow. I, unfortunately, don't think I will be able to push through tonight.

"I am so sad and sorry. I'm so upset, but of course, obviously, you will be refunded," she apologised in an Instagram video.

It also showed her using a device to help her breathe.

People magazine reported that Grande, 26, has not been in good health for more than three weeks.

"I've been sick since the last London show. I don't know how it's possible, but my throat and head are still in so much pain... and it's difficult to breathe during the show," she revealed in an online post last Saturday.

"I'm on all the meds, getting IV drips, doing everything I possibly can to pull through."

There is no word yet if her show today in Atlanta will proceed, but veteran singer Barbra Streisand, 77, had some advice for Grande.

Streisand tweeted: "Take a strong vitamin C drink with some Manuka honey and, of course, get some chicken soup."