The 18-year-old, who is widely considered one of the most promising talents in English football, is a product of the Chelsea Academy and although he has yet to make his first team competitive debut, he was involved in the pre-season tour of Asia, following an impressive year on loan at Watford.

On signing his new deal, Chalobah said: 'It is great for me that Chelsea are willing to give me such a long contract, it is a big confidence boost.

'I think I have developed a lot as a player but I know I must continue to improve to earn a place in the Chelsea team and with my future settled, I can concentrate on doing that.

'Watford was a great experience, I learned about playing in front of a crowd every game and so many other lessons that there are too many to list. Training with Jose Mourinho and the Chelsea squad this pre-season, every session has been different with something new to take on board. I've enjoyed it a lot.

'I would like to thank all the coaches who have helped me throughout my time at Chelsea.'

Jose Mourinho added: 'He's a very, very good player and I like him very, very much. I am very impressed. For sure he is a Chelsea player.'

Chalobah, who is comfortable operating in central defence or in midfield, has been captain of the Chelsea youth and reserve teams and lifted the FA Youth Cup in 2012. He has long played above his age group at international level, making his England Under-17 debut aged 14 and winning the European Championships with that team at the age of 15. He later became captain of England Under-17s and Under-19s and is now in the Under-21 squad, playing in the European Championships in Israel in the summer.

In February he was named England Men's Youth Player of the Year at an FA awards ceremony.

Playing his club football last season in the Championship, Chalobah made 42 appearances at Watford as they reached the play-off final at Wembley, and he was named the Football League's Young Player of the Month for April.

In the summer he played for the Chelsea first team in Thailand, Malaysia and Indonesia.