Sia is challenging Mike Posner for this week’s Number 1 single

Plus there are new entries from The Vamps, Galantis and AlunaGeorge on this week's Official Chart Update.

Mike Posner is facing some serious competition from Sia on this week’s Official Singles Chart.

The singer-songwriter’s current Number 1 I Took A Pill In Ibiza is leading the way on today’s Official Chart Update, but Sia’s Cheap Thrills continues to surge up the Top 40, up two places to Number 2.

Cheap Thrills has already given Sia her biggest UK chart hit as a headline artist – can she land her first headline Number 1 by this Friday? The Australian star previously hit Number 1 as a guest on David Guetta’s Titanium in February 2012. Click here to check out her full UK chart history.

MORE: Check out this week's Official Chart Update Top 100 in full

Meanwhile, Fifth Harmony’s Work From Home slips from 2 to Number 3, Lukas Graham’s 7 Years is at 4, and Zara Larsson’s Lush Life completes the Top 5.

New entries and high climbers

Two tracks are set to hit the Top 10 for the first time this week: Alan Walker’s Faded is up four places to Number 7, and Joe Jonas-fronted band DNCE leap 17 to 10 with Cake By The Ocean.

The Vamps are on course to land their seventh Top 40 hit this week with their new OMI collaboration I Found A Girl, currently at Number 20, and Meghan Trainor continues to scale the tally with No, up five places to 25.

Further down, Galantis’ new single No Money debuts at 32, and two tracks look set to climb into this week’s Top 40: AlunaGeorge’s I’m In Control (38) and Years & Years’ Desire (39).