World Triathlon on Tuesday said the Paris Olympics men's triathlon event will be postponed by a day, after tests showed the water quality in the River Seine was not up to standard.

The development means Hong Kong's Jason Ng is now scheduled to compete on Wednesday at 4.45pm. He was originally going to race at 2pm on Tuesday.

"The tests carried out in the Seine today revealed water quality levels that did not provide sufficient guarantees to allow the event to be held," World Triathlon said in a statement, adding the International Olympic Committee, Meteo France and Paris officials were involved in conducting the water tests.

"Unfortunately, meteorological events beyond our control, such as the rain which fell over Paris on 26 and 27 July, can alter water quality and compel us to reschedule the event for health reasons."

The women's triathlon event will also take place on Wednesday, with World Triathlon saying both events are subject to future water tests.

A Paris based hydrologist had earlier told RTHK that rainstorms in the 24 hours before a swimming event in the Seine could wash storm water off the land surfaces around the city, bringing pollution with it.