National Search and Rescue Agency head Bambang Soelistyo said the object – 9.8 metres long, 1.1 metres wide and 0.4 metre high – has been located on the seabed.
Nine ships have been sent to the area to continue the search, Soelistyo was quoted as saying by Xinhua.
The latest finding has made the total number of located objects to five, as four others were found Saturday. The biggest one among them measures 18 meters long.
The Airbus A320-200 aircraft with 155 passengers and seven crew members aboard went missing soon after taking off from Surabaya Dec 28 en-route to Singapore’s Changi airport. The debris were spotted last Tuesday.
It is believed to have crashed in the Java Sea, near Karimata Strait, some 153 km from Pangkalan Bun in Central Kalimantan province in Borneo island.
Earlier in the day, a pinger locator was deployed to find the black box of the plane.
The countries helping in the multinational search efforts, besides Indonesia and Singapore, are the US, Japan, China, South Korea, India and Russia.
So far, 31 bodies have been fished out of the waters, 30 of which have been transported to Surabaya for identification
The first victim was identified last Thursday.