International Olympic Committee vice president John Coates has hit out at organisers in Brazil for their failure to keep their preparations for the 2016 Rio Games on schedule.

Coates has revealed to delegates in an Olympic forum in Sydney that construction on some venues is yet to get underway, while water quality is also a worry.

"The IOC has formed a special task force to try and speed up preparations but the situation is critical on the ground," Coates told The AP.

"The IOC has adopted a more hands on role, it is unprecedented for the IOC but there is no plan B. We are going to Rio. I think this is a worse situation than Athens [in 2004]. It's the worst that I've experienced.

"We have become very concerned. They are not ready in many, many ways. We have to make it happen and that is the IOC approach, you can't walk away from this."

This is not the first time that Brazil has come under scrutiny with regards to major sporting events as a number of delays have also slowed preparations for this summer's World Cup.