Anchorage, Alaska - Royal Dutch Shell has started drilling in the Chukchi Sea off Alaska's northwest coast.

Company spokesperson Curtis Smith says preliminary work for an exploratory well began on Sunday morning.

Interior Secretary Ken Salazar announced on August 30 that Shell would be permitted to begin preparation work at the site even though the company's spill response barge has not been certified and is not positioned nearby.

The company is authorised to drill narrow pilot holes down to about 450m below the ocean floor and roughly 1 200m above an anticipated petroleum reservoir.

The company also is authorised to drill a 12-metre-deep mud-line cellar that will hold a blowout preventer.

Shell Oil paid $2.1-billion for Chukchi leases in 2008. - Sapa-AP