A BMX test event for next year's Rio Olympics was postponed until Sunday after riders refused to take part due to safety concerns.

The course was designed by Tom Ritzenthaler, who was responsible for the last two Olympic tracks in Beijing and London.

However, riders said some of the jumps on the course were too high.

The event, originally scheduled for Saturday, is now set to take place on Sunday with a remodelled course.

"We shouldn't have to 'race' on such sub-standard tracks," British rider Liam Phillips, a BMX supercross World Cup champion, posted on Instagram.

"Although I feel the sport took a step backwards with the riders refusing to ride, it was extremely necessary for the riders' safety.

"We, more than anyone else, want a platform to showcase the sport of BMX."

The BMX course is another cause for concern for Olympic organisers.

Earlier this year reports suggested that the waterways in and around Olympic and Paralympic venues are polluted with high levels of viruses and bacteria from raw human sewage.