Carlton have locked up classy defender Jacob Weitering until the end of the 2021 AFL season after the No.1 draft pick agreed to a four-year contract extension.

The 18-year-old joins Kade Simpson, Jack Silvagni and Levi Casboult in re-committing to the club in the past week.

Weitering signed a standard two-year deal when he was picked first overall at the 2015 draft, but was offered the new contract after impressing in 20 games in his debut season.

“It has been a thoroughly enjoyable first year of football and having that initial taste of senior footy just makes me more hungry to go out there and give it my all for my teammates and this club,” Weitering said.

“It’s an exciting time for the Blues and I really believe in what we are building at the club under Brendon Bolton, the broader coaching panel and my teammates.

“I’m very thankful to the club for this opportunity.”

Casboult and Simpson agreed to one-year deals to remain at the club in 2017, while Silvagni has signed to stay with the Blues until the end of the 2018 season.

Michael Jamison, Andrew Walker and Cameron Wood have already announced their retirements while Clem Smith, Matthew Dick and Jayden Foster have been delisted.