Environmental protection will receive top priority on two Chinese naval vessels that set sail on Thursday for the Gulf of Aden on a new anti-piracy mission.

The destroyer Guangzhou along with the supply ship Weishanhu, carrying more than 800 soldiers, left a port in Sanya.

"All waste will be strictly kept by category and we will not leave one single piece of trash in the sea," said Captain Li Ping, of the Guangzhou.

There are facilities on the two frigates to recycle and dispose of both solid and liquid waste, which guarantees minimum pollution. Food preparation is also environmentally friendly.

The frigates are expected to arrive in the Gulf of Aden by mid-March, where they will take over from the Maanshan and the Wenzhou. Another frigate, the Chaohu, will remain with the fifth flotilla.

The first flotilla of Chinese warships was sent to the Gulf of Aden 14 months ago after the UN called for stronger naval action to battle piracy near Somalia.

Xiao Fei, 30, was at the port with her twin 6-year-old sons to see off her husband Yuan Hanhui, 33. "My husband spends most of the year at sea and we don't see a lot of him. My only hope is for them to return home safely," she said.