HONG KONG, Aug. 21 (Xinhua) -- Thirty-four competitors started their race in the Olympic individual jumping final at the Shatin Equestrian Venue on Thursday night despite a possible disruption by approaching typhoon Nuri.

    "We will not proceed if it becomes hazardous for horses, riders and spectators," Prof. Leo Jeffcott of Britain, Foreign Veterinary Delegate, told a press conference on Thursday.

    However, there was a reasonable chance the weather would hold up and the competition could be completed during the evening.

    Meanwhile, the International Equestrian Federation (FEI) announced here Thursday that four rider-horse combinations have been banned from competing in Thursday's show jumping individual competition for testing positive in doping or positive medication cases.

    The four combinations are Bernardo Alves of Brazil (Chupa Chup), Christian Ahlmann of Germany (Coster), Denis Lynch of Ireland (Latinus) and Tony Andre Hansen of Norway (Camiro).

    FEI said that confirmatory analysis of the B-samples will be carried out very shortly according to the accelerated procedure in place for the Olympic Games.

    Mexican rider Antonio Chedraui has withdrawn from the final because his horse DON PORFIRIO failed to pass the ground jury's second inspection on Wednesday.

    After the Round A competition in the first phase, 20 qualified riders will progress to Round B to decide the medals.

    All competitors start from zero points, but the three qualifying rounds gave an indication of form.