Australian tennis star Nick Kyrgios has claimed he was racially abused by sections of the crowd during Saturday's loss to Andy Murray in the Stuttgart semi-finals.

Kyrgios was penalised a point and then a game for unsportsmanlike conduct early in the second set, smashing a racquet before an angry exchange with a group in the crowd.

The 27-year-old, who is of Greek origin, said he had been the victim of racism.

"When is this going to stop? Dealing with racist slurs from the crowd?" Kyrgios wrote on Instagram.

"I understand that my behaviour isn't the best all the time, but 'you little black sheep' 'shut up and play' – little comments like this are not acceptable.

"When I retaliate to the crowd I get penalised. This is messed up."

After the tournament supervisor was called, Kyrgios merely went through the motions on court as Murray took complete command to secure a 7-6, 6-2 victory in 93 minutes.

Murray will play his first grass-court singles final since winning Wimbledon in 2016 when he plays second-seeded Italian Matteo Berrettini in Sunday's final.

Murray stunned Stefanos Tsitsipas in the quarterfinals on Friday, the first win for Murray in six years against an opponent ranked in the top five.

It's the second final of 2022 for Murray, who lost to Aslan Karatsev at the hard-court Sydney Tennis Classic in January, and the first time that he has reached two finals in the same season since 2017. Murray, who has struggled to get back to his best following hip surgery, last won a tour singles title at the European Open in Belgium in 2019 and has a 46-23 record in finals.

Berrettini prevailed 7-6 (7), 7-6 (5) over Oscar Otte in a tight match with no breaks of serve. Berrettini saved a set point in the first-set tiebreaker and needed three match points to close out the win.

Murray and Berrettini each won one of their two career meetings, with Berrettini the victor in their only grass-court match at Queen's Club last year.

- With AP