Johannesburg emergency services continued the search for a worker trapped under a collapsed office building in Roodepoort on Friday morning, police said.

"The search started again this morning at 6am," said Inspector Karen Jacobs.

She said rubble was still collapsing into the basement area as heavy equipment was used to clear the area.

"The site is still quite dangerous," said Jacobs.

Half of the nearly-completed office block in Little Falls was destroyed when the top two stories collapsed onto the bottom storey on Thursday.

One worker was killed and 14 injured.