China's first aircraft carrier has set off for its 10th sea trial after a month's rest but may encounter Typhoon Bolaven which was sweeping along the same route yesterday.

Five tugboats towed the carrier out from the port of Dalian in northeast China's Liaoning Province to sea at 1:30pm on Monday. The carrier started its main engines at around 3:15pm and set out alone.

Its depot ship, No. 88, remained at port, an indication that the sea trial wouldn't last too long.

A restricted zone set up by the Liaoning Maritime Safety Administration "for military exercises" in the north Bohai Sea is in effect until tomorrow.

There was also no farewell ceremony like those ahead of each previous sea trial, another indication, according to China News Service, that there is nothing special about these sea trials.

Twelve poles could be seen on the left side of the carrier's deck and another two on the right, according to China News Service photographs, which may be used as markers for pilots landing aircraft on the deck.

The carrier may be commissioned later this year, but it would not have combat ability until 2017, Li Jie, a researcher of the China Navy Military Academy and a senior colonel, said yesterday.

"Normally, it will take three years for an aircraft carrier to be commissioned after its first sea trial and another five to eight years to be able to combat in a battle," Li said.

He said that was because an aircraft carrier could not conduct missions alone, but needed protection and support from a fleet including frigates, destroyers and cruisers. Some submarines were also necessary for scouting and antisubmarine tasks.

A US aircraft carrier is normally accompanied by two missile cruisers, two frigates, two nuclear-driven submarines and a depot ship.