Hero bystander helps rescue Melbourne sisters struggling in whirlpool

Two young girls are lucky to be alive after getting caught in a whirlpool at a popular Melbourne beach.

Tyla Reid, 22, saw the pair struggling and rain into the water at St Kilda Beach to help, pulling one of the sisters to safety while police officers helped the other.

Reid said he and his friends had been walking along the beach and spotted the mounted police looking over the sea wall.

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"We wanted to pat the horses and we see these two heads pop up from the other side of the sea wall," he said.

"They're screaming for help.

"I pretty much dropped my backpack and went straight into the water."

Reid had no second thoughts as he charged into the water to save the young girls.

"I know I'm a good swimmer. I was more than capable of helping the two girls," he said.

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The girls were grateful to have been rescued from the terrifying situation and told Reid how thankful they were.

"I'm just happy they're safe and sound on the beach," he said.

Superintendent Wayne Newman said the police officers and the public's response was "heroic".

Acting Sergeant Samantha Christian and Leading Senior Constable Emma Sharp were the officers involved.

It comes as Victoria has seen a spate of water tragedies over the Christmas weekend with three people drowning.

It has sparked a warning from authorities about water safety as Victoria experiences warm temperatures.

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Life Saving Vic's Kane Treloar said the fatal drownings and non-fatal drownings change the lives of the victims and families forever.

"We understand people want to come to the beach. It's been a long time since we've had the opportunity to enjoy the beach," he said.

"We're asking people to think about their safety because we want everyone to come home at the end of the day."

Treloar said to think about where to swim and if it is safe for your skill level, don't swim alone and don't drink alcohol and swim.