Idled containers in some Chinese ports have caught international attention lately. Industry insiders say companies place their containers where they anticipate demand will rebound the fastest for global shipping.

The international shipping companies taking the initiative to position idled containers at ports in China are standing by for a demand rebound, said Yu Jianhua, minister of the General Administration of Customs of China, at a press conference on Monday.

The ready-to-go containers also, to some extent, show that the international market is optimistic about China's export capacity going forward, Yu added.

Yu also attributed the pile-up of empty containers at ports to the relatively low storage costs, a large number of empty containers flowing back since the pandemic eased abroad, coupled with seasonal factors.

The container shipping market boomed in 2021 and produced 13 percent more containers around the world, triple the amount in normal years, according to Drewry, a maritime consultant.

Drewry data showed that about 4.1 percent of the global container fleet was idled in February.

"It makes sense to be close to the main export centers, to be in a ready-to-go position," Simon Heaney, senior manager of container research at Drewry, told Bloomberg.

This echoes Frank Andersen, head of Asia at maritime data provider Shipfix. Andersen said in the same report that owners are dispatching their empty ships close to where they expect demand to rebound the fastest. He also noted that it's a lot cheaper to park a vessel in China compared with Singapore.

China's exports of goods increased 0.9 percent year on year to 3.5 trillion yuan ($506.1 billion) during the first two months of 2023, customs data showed.

Specifically, the volume of export containers has been increasing continuously since late February, according to Yu.

The average daily container throughput at the largest container loading and unloading terminal in Ningbo Zhoushan Port reached 31,600 TEUs since March, rising 14.5 percent compared with the same period last year, port data showed.