Road racing is mourning the death of Portuguese rider Luis Carreira who was killed in an accident during qualifying at the Macau Grand Prix in Southern China this morning.
Mr Carreira, 35, was involved in an incident at Fisherman's Bend. No other competitor was involved.
He succumbed to his injuries and the session was postponed until Friday.
Isle of Man TT legend John McGuinness was among a stream of riders expressing their shock via Twitter.
Ian Hutchinson – who finished on the rostrum in third place at Macau in 2011 – also took to the social networking site to pay tribute, saying: “Very sad news of the passing of luis carreira… My thoughts go out to his family and friends.”
Tyco Suzuki's Conor Cummins said: “RIP Luis. Shocked to hear the news. God speed,” while Martin Jessopp tweeted: “After riding past Luis I kept hoping for the best but this sport can be so cruel. R.I.P. fella.”
Mr Carreira, who was riding a Suzuki for the Bennimoto Raider-Cetelem team, was an experienced competitor at Macau, where he has been a regular since 2004.
He also competed at the Isle of Man TT, making his debut on the Mountain course in 2009 and achieving a best result of 13th in the Superstock event in 2011.
This year, he finished 24th and 22nd in the Superbike and Senior races at the TT.
Isle of Man Government TT and Motorsport Development Manager Paul Phillips added his thoughts on Twitter, saying: “Such sad news about Luis. One of the nicest men I have ever met in motorcycling. A real gentleman and a very talented rider.”
Fellow Portuguese rider Nuno Caetano has withdrawn from the event following the death of his compatriot and friend.
Another free practice session will be held at Macau tomorrow morning at 7.30am followed by qualifying in the afternoon at a time yet to be confirmed.
Saturday's race is scheduled for 15-laps.