Prime Minister Tony Abbott and his Singapore counterpart Lee Hsien Loong were photographed flipping steaks at one of the '50 BBQs' hosted by Singapore's Australian High Commission to celebrate 50 years of diplomatic relations between Singapore and Australia on Sunday.

But just hours before the first steak was set to sizzle, locals were outraged to learn that attendance would be restricted by a ticketing system controlled by the People's Association, the grassroots supporters of the ruling People's Action Party.

'50 BBQs' was billed as an open, public event where Singaporeans would be treated to an Aussie-style BBQ where 10,000 beef and lamb steaks would be served at 23 sites across the island.

But on the morning of the event a post on the Australian High Commission's Facebook page announced that entry at some of the BBQs would require a ticket distributed by the People's Association.

"Many locations are ticketed by the People's Association to ensure there's enough food for all. But we've been told some spare coupons are set aside for those who just show up," according to the Facebook post.

The page was bombarded with angry comments from Singaporeans who felt cheated by the ticketing system implemented at the eleventh hour.

"We don't even know where to get the tickets because it wasn't stated we need to get the tickets. And now, like you said, tickets are all taken," one commenter said.

At the Bishan Park site, where Mr Abbott wielded the BBQ tongs,  locals with no tickets were only invited to partake once all the ticketed attendees had eaten their fill, according to commenters.

"Why wasn't this announced earlier that those ticketless residents from neighbouring estates were only entitled to leftovers from 8.30pm onwards? Disappointing," said one commenter.

"'First come, first serve,' my foot. 'Open to public,' my foot. Please eat your own words. Most of the locations requires coupon. Please stop posting nonsense like 'open to public' or 'first come, first serve'. All are just inaccurate information passed down," said another.

Several posts accused the People's Association of diverting tickets to supporters and refusing access to non-members.

"The idea was good but shame it ended up as an ugly spat between the haves and the haves-not," wrote one commenter.

"A fantastic initiative undermined by the ruthlessly mechanical PA machine rejecting all non invitees," read another.

"PA, you should clearly state it's for your selected members AND NOT OPEN TO PUBLIC," wrote a third commenter.

The Australian High Commission did not respond to requests to comment.

The People's Association declined to comment.