A teenage boy has been left with serious injuries after being stabbed and assaulted in broad daylight by a group of youths in Mordialloc on Friday.

The 15-year-old was walking along Main Street and reached Pompei’s Landing park before being approached by five unknown young people at about 2.30pm on Friday.

One of the youths demanded the victim's jacket, police said, before punching him in the head repeatedly.

Another male then pulled out a knife and stabbed the victim before all five fled south under the park tunnel, towards Park Street.