A baby boy has broken the record for the biggest baby born at a Melbourne hospital almost double the weight of a regular newborn.

An ultrasound at 35 weeks was a little misleading, estimating Maoama Ala's weight at 4.5 kilograms. He was born almost 2kgs heavier on Tuesday at Sunshine Hospital, at 39 weeks.

The fourth child for the Tarneit family, who are originally from Samoa, tipped the scales at a record-breaking 6.3kgs, and measured 60cm long.

View photos Maoama Ala has broken the record for the biggest baby born at Sunshine Hospital, weighing almost double a regular newborn. Source: 7 News More

That's almost double the average Australian baby, which weighs about 3.3kg.

“Everyone was asking me, ‘Are you having twins?’ And I was like, ‘I wish’,” mum Teuaililo Ala joked.

“The main thing was not his size, but he was coming out a healthy and happy baby,” she told 7 News.

His parents thought they were prepared for a newborn, but Maoama is already wearing clothes meant for three to six-month-old babies.

View photos Maoama is the fourth child for the Ala family, who are originally from Samoa. Source: 7 News More

Obstetrician Dr Lauren de Luca said the newborn was “off the charts”.

“Once she knew we were expecting such a big baby, she did decide for an elective Caesar, which is a sensible option," Dr de Luca said.

The Ala family already have nine-year-old twins and a six-year-old boy, who are eager to dote on their baby brother.

View photos Nine-year-old twins and a six-year-old boy are thrilled with their little brother. Source: 7 News More

After spending three days in hospital, Mrs Ala prepared to head home on Friday.

Incredibly, the big delivery hasn't deterred her from wanting more kids, and she is planning on having a fifth child in the near future.