"The public beach near our home is closed and there is a crew working with shovels and plastic bags to clean it," a resident said.

The origin of the slick was not clear and coast guard officials could not be reached for comment.

Environmentalists say most oil pollution on the beaches is due to spillage from oil tankers in the Gulf. An estimated 50,000 vessels passing through the shallow waterway discharge around 30 million cubic metres of ballast water every year, according to the Emirates Environmental Group.

Saturday's slick appeared to be concentrated in the Jumeirah area, site of the Burj al-Arab and Jumeirah Beach luxury hotels, while hotels further east in the Marina area were not affected, according to staff called by Reuters.