A teenage boy was allegedly slashed with a machete after five men gatecrashed a house party in Sydney's east yesterday evening.

Emergency services were called to an address on Carnegie Street in Chifley about 8.25pm following reports of a brawl.

Police were told five males had entered the party uninvited while armed with machetes.

One witness told 9News the armed men were dressed in ski masks.

They allegedly fled the scene before officers arrived.

Paramedics treated a 16-year-old at the scene for laceration to his back and legs and he was taken to Royal Prince Alfred Hospital in a stable condition.

A crime scene has been established and police have commenced an investigation into the incident.

Anyone with information is urged to contact police or Crime Stoppers on 1800 333 000.

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