First it was fame on Instagram, now Guinness World Records is calling - but to placid Melbourne house cat Omar, it's all just another day in the office.

Three-year-old maine coon Omar is reportedly in the running to become the longest cat in the world - a record currently held by a maine coon from the UK named Ludo who was measured at 118.33cm in 2015.

Owner Stephy Hirst, from Croydon in Melbourne, told the Maroondah Leader she started an Instagram account for her giant cat a couple of weeks ago and before long he had been featured on Cats of Instagram, which has more than 8 million followers.

And once you've been on Cats of Instagram, it appears the sky is the limit.

Ms Hirst said she was contacted by Guinness World Records who said Omar could be the longest cat in the world. She has sent his measurements in for verification.

At 120cm long and weighing 14kg, he's already about three times the size of the average cat.

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"(Omar) was tiny when we got him but then he just started growing and was 10kg at one year old," Ms Hirst said.

"We thought he might be (the longest cat in the world) but we hadn't done anything about it because he might not be fully grown yet."

Omar eats a diet of kibble and raw kangaroo meat and enjoys naps on the couch or trampoline.

He also lives with two Shetland Sheepdogs Penny and Rafi who he has long outgrown.