Analysts say new construction industry data could show the end of the boom.

The Australian Industry Group Performance of Construction Index has fallen to a 20-month low, down 5 points to 45.9

Peter Burn, head of policy at the Australian Industry Group, calls it; “A quite a noticeable contraction in activity”.

“The performance of construction activity is made up of four sub-sectors, and each of them is in negative territory in October.

“House building, apartments, commercial construction, and engineering construction — all negative.”

Mr Burn expects construction activity will continue to slide.

“I think it's probably constructors going; ‘Well we're less sure about the ability to sell the next batch, so we'll hold off any plans that we have, or we won't put new plans in place’, and they might just shelve plans altogether,” he said.

Peter Kerras from Colliers International says Sydney is still going well.

“I can tell you we have more business than we've ever had at the moment,” he told the ABC.

“We've got seven launches at the moment prior to Christmas, and we've got interest in everything.

“I'm a bit sceptical when people talk about national figures, because we're in a bit of a bubble here in Sydney.

“When you tell someone in Sydney about national figures and it's a negative message, they may make the wrong decision based on that, and you might find Sydney is perfectly fine.”

The experts say construction will be affected by the earnings of the big four banks, which have dropped for the first time since the global financial crisis.

Bad loans are at their highest level since 2012.