Grandfather allegedly slashed with knife during Melbourne home invasion

A Melbourne grandfather has allegedly been slashed with a knife during a violent home invasion in Doncaster East.

The 60-year-old was staying at his son's house when they say up to seven youths broke in just after 5am this morning.

The grandfather, his 38-year-old son, daughter-in-law and 18-month old grandchild woke to the sound of the gang allegedly stealing his son's Maserati, Mercedes and Audi.

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"It happened so quick so, it's really horrible," the son said.

The father and son tried to stop the accused thieves and pull them out of the vehicles.

"We fight out the front of our house and we were fighting on the street as well," the son said.

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"I'm trying to stop them and opened the car as they're driving but didn't stop them," he added.

The grandfather was slashed in the hand during the scuffle.

Members of the group allegedly told the family "I'm going to kill you", while carrying knives.

Police were later called to Ryelands Drive to reports of two rival gangs fighting on the street.

The altercation flared up again inside Narre Warren Coles Express Service Station just before 7am.

Witnesses have told 9News more than 10 youths were fighting inside with machetes and poles, forcing staff and customers to barricade themselves in a backroom as they waited for police to arrive.

Eight teenagers, who police have described as "teen gang members", have today been arrested over the incident.

Police said an 18-year-old man from one of the groups was injured and subsequently transported to hospital with serious but non-life-threatening injuries.

A 16-year-old boy from Wallan, 17-year-old boy from Cranbourne North and a 17-year-old boy from Narre Warren were arrested n Narre Warren North Road just before 8am.

A further five teenagers were arrested at a shopping centre in Casey shortly after midday.

This includes an 18-year-old man from Mulgrave, an 18-year-old man from Cranbourne North, a 17-year-old man from Doveton, a 15-year-old male from Doveton and a 15-year-old-male from Cranbourne South.

Police said the exact circumstances surrounding the incidents are being investigated and the teenagers in custody are currently assisting police with their enquiries.