Pham Hong Manh, manager of Hai Phong shipping firm T.S. Container Lines, said his company has reduced shipping from China since January 19.

It used to ply up to 13 times a month to Chinese ports, but the figure was down to eight last month and to seven this month, he said.

Ships are docking at other ports outside China, which accounts for 40 percent of international shipping in Vietnam, but this pushes up costs, he said.

"Our shipments have fallen by 30 percent year-on-year due to the outbreak. We estimate our losses at millions of dollars."

Vietnam’s biggest shipping firm, Vinalines, is also struggling as shipping activities in China and some other countries have dwindled. Many of its ship are lying idle in ports.

The company, formally known as the Vietnam National Shipping Lines, estimated shipments in the first six months could fall by 15 percent year-on-year.

Its revenues could fall by VND992 billion ($42.7 million) and profits by VND224 billion ($9.6 million) in the period, it estimated further.

The epidemic outbreak has meant there are fewer personnel to operate ports in China, resulting in less traffic to all countries, including Vietnam.

Quy Nhon Port in central Vietnam now operates only 20 days a month instead of 30, with shipments falling by 15 percent. Last month it handled 100,000 tonnes less than targeted.

Vietnamese ports handled 655 million tonnes of cargo last year, up 14 percent from 2018, according to the Vietnam Maritime Administration.