NBA star Ben Simmons has reportedly left hundreds of children devastated after sneaking away from a basketball camp and refusing to sign autographs or take pictures with waiting fans.

The 23-year-old hosted two training sessions for hundreds of children aged between seven and 17 at Hills Basketball Stadium in Castle Hill, Sydney, on Sunday.

But Australia's richest athlete - who recently signed a $243million, five-year deal with Philadelphia 76ers - left the stadium without greeting the hundreds of youngsters who had gathered outside before driving away in a Mercedes, the Daily Telegraph reported.

Ben Simmons is pictured at his Basketball Camp in Melbourne on Sunday July 28. He reportedly snuck out of his Sydney event on Sunday

Fans of the NBA star congregated at an outside doorway where a Mercedes was parked after the event, in the hope of meeting the sporting icon.

Simmons described the camp as 'amazing', 'insane' and the 'best' of the year, while urging fans to return in 2019.

Khan, who did not want to share his last name, said he was disappointed he didn't get to meet Simmons.

'Look at these kids here. They haven't seen him and he just ran away,' the 19-year-old said.

'I really wanted a photo of him, I've been a fan since he was a rookie. It was a bit s**t.

'I spoke to one of the coaches and he said he hardly spent any time on the court with the people who paid the money.'

According to Simmons' website, the basketball camp is a raging success with young fans learning important skills.

'The camp this morning was fantastic, my son absolutely loved it and has not stopped smiling since we pulled into the car park this morning,' one review read.

'The quality of instruction and organisation was great and the overall atmosphere felt good,' said another.

The 23-year-old hosted two training sessions for hundreds of children aged 7-12 and 13-17 out of Hills Basketball Stadium in Castle Hill, Sydney, on Sunday

The description for the Sydney and Melbourne camps read: 'Ben is excited to host two camps which are open to Girls and Boys aged 7 to 17'.

In an Instagram story from Sunday's event, Simmons sat with camp attendees for a Q&A after the activities.

Simmons, who was born in Melbourne and grew up in Newcastle, first launched his camp in Melbourne.

Simmons jetted into Sydney on Saturday and was snapped walking through the terminal and posing with fans for pictures.

His visit to Australia has dominated the headlines after he reportedly walked out of an interview and was denied entry from Melbourne's Crown Casino.

Footy icon Chris Judd said Simmons 'cracked it' after former AFL star Campbell Brown referenced the Crown Casino incident in an interview this week.

In an Instagram story from Sunday's event, Simmons sat with camp attendees for a Q&A after the activities

Simmons claimed he was racially profiled by Crown Casino on Monday August 5

Simmons claimed he was racially profiled by the casino on Monday August 5 and denied entry, but Judd said the topic was off limits during his chat with Brown.

'It was bordering on a little bit safe, and then 'The Dog' [Brown] thought it was time to bring in a little bit of sizzle,' the West Coast Eagles legend told Triple M's The Friday Huddle.

'He said 'we've got a fair bit in common you and I. You drive a Maserati, I drive a Toyota Kluger. You're worth $250million and I'm borderline unemployed.'

''The last thing we have in common is we've both been denied entry to Crown.''

A spokeswoman for Crown Casinos told Daily Mail Australia the group were allowed in, and denied the allegations made by Simmons.

'Crown strenuously rejects reports that it discriminated against a group of visitors last night,' she said.

Judd said Simmons failed to see the funny side of Brown's joke - simply responding with 'this interview is done'.

Simmons appeared on Saturday at a Melbourne game to watch his friend and Demons star Christian Petracca in action against Collingwood, and was earlier this week seen trying his hand at kicking a footy.