A man went through a plate glass window and another was injured by a weapon after a fight broke out at Napier McDonald's last night.

Two young men were taken to Hawke's Bay Hospital by St John Ambulance with non life-threatening injuries, said Detective Sergeant Darren Pritchard.

Several customers were in the restaurant when the fight broke out and police believe more than the two injured men were involved. CCTV images are available.

One of the two was known to police, the other was not, Pritchard said.

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At least one weapon was recovered.

"No, it wasn't a plastic knife," Pritchard said.

The dine-in area and main counter of the restaurant were closed while police investigated, but McDonald's staff were kept busy dealing with increased traffic at the drive-thru.

Staff at the fast food restaurant were shaken after witnessing the violent outburst between teenagers.

The restaurant is staffed mainly by young people, family of whom expressed concern on a facebook thread, including parents worried about the traumatic effect on teenagers and children who witnessed the violence.

One commented her daughter was so traumatised she didn't want to go back.

"Poor girl," another responded. "She has to live with that. Nobody deserves to see that crap."

No arrests have been made yet as police still needed to speak to a number of witnesses.