As the race for this year's Christmas number one goes down to the wire, pop icon Justin Bieber has thrown his weight behind the NHS Choir rivalling him to top the tree. Bieber has publicly urged people to support Lewisham and Greenwich NHS Choir's charity single "A Bridge Over You".

The competition between the choir's single and Bieber's "Love Yourself" is neck-and-neck, with just a few hundred sales between them. The Canadian singer, who champions state healthcare, tweeted: "Let's do the right thing and help them win. It's Christmas." He also wished the group good luck in the battle for top spot.

At the time of his tweet on 23 December, the NHS choir had managed to dramatically slash Bieber's lead, which had been reduced from 7,000 to 662 sales in a 24-hour period. Sales will stop being counted at midnight tonight (24 December). The choir is made up of a range of NHS staff, including doctors, physios, nurses and porters.

The festive number one is calculated by combining sales and streaming figures and is set to be announced on Radio 1 on Christmas day. "It's just ridiculous that it's the NHS versus Justin Bieber, but that's all in the jolliness of it," choir member and doctor Katie Rogerson told the Guardian. "You don't expect an NHS choir to make the top 40 so to be honest, we're [already] massively pleased. If we got to number one, it would be insanity – but a really good version of it."

Speaking to BBC Newsbeat, Liz Steele, a physio in the stroke unit at Lewisham hospital said: "I can't believe we're actually in the charts competing for number one." She continued: "We've got some pretty tough competition so to be in this position is amazing... anything could happen", before adding that it was "just a bit bonkers" to be competing against a singer with superstar status, such as Bieber.