The City of Sydney has blamed a recent rise in rat sightings across the CBD on "unprecedented" construction work, as two restaurants in as many weeks had to close to deal with rodents.

The Sydney Westfield storefront of popular Taiwanese restaurant chain Din Tai Fung voluntarily closed on Thursday after a video surfaced of a rat scurrying around its kitchen area.

Sydney resident Lucy Hui, who posted the video and tagged Din Tai Fung Australia in the post, said it was sent to her.

"Makes me want to vomit," she wrote. "Never eating there again....and it was a favourite."