Bendigo Health emergency medicine physician Nathan Bushby said some patients may have died without the treatment from emergency room staff.

"We want to remind everybody of the importance of remaining hydrated, staying cool and looking after one another," Dr Bushby said.

"We are looking at a 40 to 50 per cent increase in our workload through purely heat-related illness."

Dr Bushby said the emergency department had seen a broader range of heat-affected people than usual.

"Predictably there are a lot of elderly people with dehydration and associated collapses and vomiting but also a lot of outdoor workers, who we don't normally see," he said.

"A number of young guys working outside on roofs or building sites have been driven to hospital with dehydration or kidney failure related to dehydration." 

Dr Bushby said the duration of the hot weather had caught people unaware.

"Typically we see one hot day but not two, three or four days in a row," he said.

"We strongly encourage people to not go outside unless you have a really good reason to do so."

Bendigo Health is expecting a further increase in patients before the heatwave is over - something that will put a strain on the hospital's resources.

"We are expecting more (patients) through to Saturday and Sunday and we have increased staffing levels an made and effort to accommodate people," he said.

Dr Bushby said there were simple things people could do to help prevent succumbing to the effects of heat.

"You need to be drinking water almost as soon as you get up and not use coffee, tea or - heaven forbid - alcohol as a substitute for water," he said.

"You need to be drinking constantly though the day. If you're feeling thirsty, long way behind where you need to be." 

High temperatures from heat exposure can cause kidney failure, muscle damage, confusion and an altered conscious state.

Dr Bushby said the symptoms of heat stroke may include someone feeling lethargic, sleepy or complaining of headaches or dizziness.