Authorities said the Shenzhen Bay Port will be closed on Saturday morning for the National Games marathon, as they called on travellers and motorists to use other border checkpoints.

The Shenzhen Bay Port will not be open to the public from 2am to 11am on Saturday.

A total of 71 runners, including five Hong Kong athletes, will participate in the 42.195km-long cross-boundary event.

The men's race will start at 7am at the Shenzhen Bay Sports Centre, while the women's race will begin 30 minutes later.

At a media briefing on Wednesday, Yeung Tak-keung, head of the National Games Coordination Office in Hong Kong, said it's all systems go for the marathon.

"We have been working very closely with our Shenzhen counterparts to make the preparations," he said.

"With the experience gained from the test events in February this year, we are confident that we can conduct the race smoothly."

He also said there could be traffic delays after the crossing reopens as some roads remain shut in Shenzhen.

Unlike the cross-border road cycling event last Saturday, there won't be a public viewing zone for the marathon because the route includes restricted zones.

On another National Games event – the triathlon – which will be held on Saturday and Sunday at the Central Harbourfront and Victoria Harbour, Yeung said while the test event held back in March was very successful, his office will make further improvement based on the feedback from mainland athletes and coaches.

Expo Drive between Legislative Council Road and Expo Drive Central was shut from 10am on Wednesday to allow authorities to prepare for the race.

In addition, some roads in Central and Wan Chai will be closed temporarily from the stroke of midnight on Saturday at the earliest.

Ninety athletes, six of them from Hong Kong, will compete in the triathlon.