"This week, we formally sought Chinese assistance to implement the deep-sea port project," economic relations secretary Mosharraf Hossain Bhuiyan told AFP.
Bangladeshi Prime Minister Sheikh Hasina discussed the plan with Chinese Vice President Xi Jinping when he made a two-day visit to Bangladesh in June, Bhuiyan said, adding Beijing's initial response had been "positive."
Bangladesh's main seaport in the southwestern city of Chittagong has been hit by severe congestion in recent months, with the average turnaround time for a container rising from three days to 11.
And the situation is likely to worsen, analysts say, as exports continue to soar -- garment shipments rose an average 30 percent year on year in July and August, according to government statistics.
The government wants Chinese help -- which could take the form of grants, concessional loans or technical assistance -- to build the new deep-sea port near the southeastern island of Sonadia, Bhuiyan said.
The government hopes the new port will become the main shipping hub for northeastern India, China's Yunnan province, Myanmar and landlocked Nepal and Bhutan.
The deep-sea port project has been in discussion for years, but Dhaka last year finalised the location and began looking for international partners.
Dhaka's decision to request Chinese assistance is likely to raise eyebrows in India, Bangladesh's neighbour and closest ally, which is concerned about growing Chinese influence in its backyard in South Asia. China is also developing port facilities in Sri Lanka, Myanmar and Pakistan, and has plans for rail projects in Nepal and Sri Lanka.
Bangladesh is also in discussions with the Chinese and Myanmar governments to build a highway connecting Bangladesh's southern port city of Chittagong with Kunming, the provincial capital of Yunnan, by way of northwestern Myanmar.