Chile's billionaire ex-president Sebastian Pinera is on track to return to office, according to partial results from a runoff election held Sunday.

Electoral authorities said the 68-year-old conservative, who previously ruled 2010-2014, had 54 percent, with nearly half the ballots counted.

That placed him comfortably ahead of leftist challenger Alejandro Guillier, a TV presenter turned senator who ran as an independent but who was backed by outgoing center-left President Michelle Bachelet.