The pop star - who has been on tour with band mates Harry Styles, Liam Payne, Zayn Malik and Louis Tomlinson - was stunned by how many fans turned out to their shows as part of their 'Where We Are Tour'.
He told Irish radio station Spin 1038: ''The shocking thing to us is that this is our first time in South America. We come down here and our fans have sold out stadiums for us. It gets us really excited. We've done some amazing shows, playing to 50/60,000 people a night.''
The 20-year-old star is also excited to be heading to his hometown of Dublin at Croke Park where they kick off the European leg of their tour on May 23 and he insists fans have a lot to look forward to when it comes to the live production.
He explained: ''It's very fun-filled, we try to have a laugh on stage and get the crowd involved, it's a must for us.
''I play guitar on nine or ten [tracks], I try and play it as much as I can. Croke is coming up in a couple of weeks and it's going to be unbelievable. It's one of the gigs that everyone is talking about, that and Wembley of course.
''They've been waiting a while since the last time we were in Dublin.''
Talking about the band's worldwide success, he added: ''We're all in the same boat, we're all from tiny little places, probably none of us had ever been to London. It's just unbelievable. We're baffled by it, it's just ridiculous, at my age as well, it's unreal [but] we're having a great time. The last two and a half weeks in South America, I never thought I'd get to countries like this.''
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