The fee was not disclosed by Chelsea but is believed to be £33m (40m euros).

The forward, who scored 23 goals for Marseille last season, scored in Belgium's last-16 win over Hungary at Euro 2016 and also came on in their quarter-final exit to Wales.

"I am delighted to sign for one of the biggest clubs in Europe," Batshuayi told Chelseafc.com.

"[My Belgium team-mates] Eden Hazard and Thibaut Courtois have told me many good things about the club, and with Antonio Conte coming in, it's an exciting time to become a Chelsea player."

The deal will see the 22-year-old forward stay at Chelsea until 2021.