NSW premier mobbed by bridge protesters

Expecting to be presented with a portrait of herself, Gladys Berejiklian arrived at a gallery northwest of Sydney to instead be confronted with a picture of community anger and frustration.

The NSW premier was mobbed by protesters on Wednesday morning as she entered the Hawkesbury Regional Gallery to unveil the portrait.

Up to 50 protesters lined the entrance to the gallery, voicing their opposition to the slated destruction of the Windsor Bridge and the nearby historic Thompson Square.

They could be heard chanting outside and in the foyer of the gallery as Ms Berejiklian unveiled the portrait upstairs.

"Thank you so much for having me here today and again I apologise for the noise outside," Ms Berejiklian told the small audience within the gallery.

Outside, protester Jan Sparkes said the premier and local member, Treasurer Dominic Perrottet, had left local residents with no other choice but to demonstrate.

"We're here because the state government, Roads and Maritime Services, our local member ... no one is listening to us," Ms Sparkes told AAP.

Local residents are pleading with the government to build a separate bypass further upstream on the Hawkesbury River to protect the bridge and square.

"We've got a historic precinct called Thompson Square that they're ploughing through, destroying it forever," Ms Sparkes said.

"It dates back to the early colony."

Ms Berejiklian, who was quick to enter the gallery as protesters swarmed her entourage, did not speak to any of the group.

Questions to the premier about the bridge and the protesters were deferred to Roads Minister Melinda Pavey, who said the bridge's redevelopment would not impact heritage buildings at Thompson Square.

"The investment into the new Windsor Bridge is long overdue and is an important road connection for residents," Ms Pavey said in a statement.

"We're continuing to speak with the local community to deliver better infrastructure for them."