The 22-year-old striker has been linked with Manchester United and Tottenham but decided to sign a new five-and-a-half-year contract on deadline day.
"I am still young," he said. "I have to work a lot and I have a lot of years to improve as a player. I am happy here and I don't have to think of anything else.
"Newcastle gave me everything. They made me professional and I have to be pleased with the club. They signed me until 2021 - five years!
"They trust in me in this deal. So I say, 'Thanks' and now work harder and prove, and show on the pitch that I deserve it."
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