The partial collapse of the roof of a Granville Street sex shop in downtown Vancouver forced the closure of some streets on Thursday morning.

Skylar Gray was working inside the store when she heard a loud crash "like the sound of bricks falling" around 3 a.m. PT.

Sex shop roof collapse blocks downtown Vancouver traffic

Traffic on Helmcken Street was blocked on Thursday morning after a building collapsed. (CBC)

Gray said she ran outside and saw the back of the building's roof had given way.

According to reports, part of the roof of the one-storey adult entertainment store gave way after a truck backing up in the alley hit some power lines attached to the building, sending a pile of bricks, metal and wood tumbling to the sidewalk.

Nobody was injured and an investigation into the cause by city inspectors is still underway.

Helmcken Street was closed to traffic between Granville and Howe streets because of the debris. The southbound lane of Granville Street was also closed, but reopened around 8 a.m.

Google Maps: Helmcken and Granville streets

Vine: video of roof collapse