Michael Knight, president of the Sydney Organizing Committee for the Olympic Games, on Wednesday said he could not rule out major accidents on Sydney's rail network during the Games, as investigations began into a fire and a collision on Sydney's disaster-prone rail network Tuesday night.

"Nobody can guarantee that during the Olympic period there won't be a derailment, there won't be a breakdown, there won't be a repetition of one of the unfortunate incidents . . . like occurred last night," the SOCOG chief told reporters at the Japan National Press Club in Tokyo.

Six people were injured and up to 80 others were forced to evacuate a train after a suspected electrical fault sparked a fire in a carriage in the Blue Mountains west of Sydney on Tuesday night.

Hours later, eight workers were injured when two freight trains collided at Port Botany, southern Sydney.

Sydney is rushing to fix its problem-plagued transport system in time for the Games, but accidents continue to occur with disturbing regularity on a system struggling to cope with existing demand.

Knight, in Tokyo to discuss Sydney's preparations for the Games in September with the Japan Olympic Committee, said contingency plans were being drawn up to use extra buses to move an expected crush of 500,000 visitors in case of accidents.

"When you are running the system 24 hours a day under loads it is not normally built for," Knight said, "it would be prudent to plan a contingency if anything goes wrong."

The city plans to run trains every 71/2 minutes around the clock -- compared to every two to three minutes during peak hour in Tokyo -- to get people to Olympic Park, 14 km west of the city center.

The new rail services chief, Ron Christie, who has reportedly admitted pressures during the Games would be "extreme" and lead to problems that could not be fixed in time, told reporters in Sydney Wednesday that the train fire Tuesday could have easily triggered a spate of crashes, the Australian Associated Press reported.

New South Wales Premier Bob Carr has admitted that Sydney's train service is "plainly unsatisfactory."

Knight, also Olympic Minister in New South Wales, took charge of the SOCOG after going through four chief executive officers. He admitted that the SOCOG still had to sell 150,000 tickets to Olympic events to break even.