Rockslides engulfed a quarry in northern Oman, emergency authorities said Sunday, with at least six workers dead and others missing.

Further slides in the wake of the deadly collapse were hampering rescue efforts at the quarry in Ibri in the Al-Dhahirah governorate, the Gulf state's Civil Defence and Ambulance Authority (CDAA) said.

Footage posted by the CDAA showed a towering cliff face crumbling onto the quarry below, creating a huge cloud of dust as workers shouted.

"The rockslides are still going on and hampering the search for missing people," it tweeted.

"So far, six dead people have been recovered and four others have been treated in moderate to critical condition," it said, without giving the victims' nationalities.

Ibri, in the Hajjar mountain chain about 200 kilometers (125 miles) from the capital Muscat, is a center for quarries, mainly marble, which often employ immigrants from South Asia.