A St John spokeswoman described the day as "hectic".

"I think it's a combination of alcohol and the hot weather," she said.

Kembla Grange racing manager Michael Craig said some racegoers collapsed while waiting in the queue for proof-of-age wrist bands before they could buy their first drinks on-site.

"There were some long queues at those stations and quite a few people went down with heat exhaustion," Mr Craig said.

An estimated 8000-strong crowd was at the racecourse for its biggest day of the year.

However, the extreme temperatures prompted a mass exodus only moments after the Melbourne Cup was run at 3pm, with four local races still to go.

"It's probably put a little bit of a dampener on the day, especially for people who were looking forward to coming out here and found that they couldn't get any real relief from the heat," Mr Craig said.

"We have measures in place for hot or humid days, but getting such oppressive conditions on Melbourne Cup Day, when we've got a capacity crowd, it's sort of beyond our limits."

About 25 police from Wollongong and Shellharbour patrolled the race venue, although there was little for them to do.

A police spokesman said crowds were well behaved.

"We've ejected probably a handful of people - that's all," he said.

Jamberoo's Luke Martignago, one of six responsible service of alcohol marshals brought in to monitor punters' compliance with Office of Liquor, Gaming and Racing regulations, observed no incidents.

"Considering the numbers we've had, they were very well behaved," he said.