A senior IOC figure insists there is no alternative to staging the 2016 Olympics in Rio de Janeiro despite chronic delays causing a "critical" situation in the host city.

John Coates, an IOC vice-president and president of the Australian Olympic committee (AOC), delivered a devastating blast at the state of Rio's preparations.

He described the preparations as "the worst I have experienced" and "worse than Athens [the 2004 hosts]" but said there was "no plan B".

Coates, a member of the IOC co-ordination commission monitoring Rio's preparations, said: "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.

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

Speaking at an Olympic Forum in Sydney, in comments reported on the AOC's website, Coates revealed that construction has not even started at some venues, that infrastructure work is significantly delayed and that water quality is a major concern.

Coates added: "The city also has social issues that need to be addressed."

"We have become very concerned. They are not ready in many, many ways."

He also claimed that Games organisers were "fobbing off" IOC inspectors when they asked for specific information, and that only two staff were working in the test event department with tournaments due to start this year.

"No-one is able to give answers at the moment," Coates added.

"Can they use the car parks in the village for recovery centres? What will be the time to take from this venue to this venue?

"All of those things, they're being fobbed off."

The IOC has not faced such a crisis with an Olympic host city since Athens in 2004, where work continued until the very last minute before it was finally able to stage the Games.

Earlier this month, sports federations demanded a back-up plan to Rio because of the chronic delays and IOC president Thomas Bach promised action to stave off the crisis, sending in Olympic Games director Gilbert Felli as a troubleshooter.

Rio's mayor Eduardo Paes has hit back at the complaints, saying the sports federations were making too many unnecessary demands but that he will not bow to their pressure.