No matter how many new technologies are used for border inspections, the experience of immigration officers is still key to spotting suspicious activities, said Xu Chengzhi, an immigration inspection officer at Heihe port, Heilongjiang province.

Xu has been an officer with the China Immigration Inspection office at the port－which links Heihe and Blagoveshchensk in Russia－since 2003, and he's seen how technology has been updated to make border inspections more efficient.

"But it's still down to the officers to ensure that no one can, or dares, exit or enter China illegally," the 36-year-old said.

The distance between the passenger ferry ports of Heihe and Blagoveshchensk is only about 650 meters, making Heihe the closest Chinese port to Russia.

As head of a passenger inspection team, Xu walks back and forth all day along the yellow line behind the inspection desks in the ferry port's departure hall, dealing with irregularities reported by officers.

"There is no room for error, because the consequences could be severe, so we have to be on high alert all the time," he said.

He has memorized anti-counterfeiting details of more than 20 kinds of passports and 30 visas commonly seen at Heihe, as well as basic information about the countries from which most passengers originate. Armed with that knowledge, he has spotted more than 30 people trying to cross the border illegally, and prevented 16 foreign criminal suspects from entering China.

In May last year, he spotted a Russian woman, who had previously been refused entry to China after overstaying her visa, trying to use a different passport to cross the border.

She claimed it was the first time she had visited China, but the record on her new passport showed otherwise.

Moreover, the name on her passport was different to the one on her Russian ID card, Xu said, explaining why the woman had seemed suspicious. In fact, she had remarried and changed her surname, then applied for a new passport in the belief it wouldn't show details of her previous trips overseas.

"Although the number of people passing through Heihe has risen in recent years, people should not think we will slack off during inspections just because our workload has increased," Xu added.

A busy year

After the Heilongjiang River began to freeze, the busy port was closed on Nov 5. However, work is far from over for Wang Jun, an immigration inspection officer, and his colleagues, who cleared cargo trucks carrying a record volume of goods heading to and from Blagoveshchensk during the ferry season.

Cargo shipments and inspections resumed on Dec 4 after the river froze completely and a "floating bridge" was established for freight trucks.

"It's been a busy year for us, as the freight volume passing through the port has increased significantly," said Wang, who has been an immigration officer for more than eight years.

"In the summer, ferries transport passengers and freight trucks. After floating ice forms on the river, hovercrafts carry people across. In deep winter, cars and trucks can drive across the floating bridge. There are so many ways to cross the river from Heihe, which is unique in China."

Last year, the largest volume of goods passed though the port since it opened in 1987. The number reached 579,000 metric tons, a rise of 51 percent year-on-year. Soybeans and related products are among the most popular imports, according to the inspection authority, which came under the management of the National Immigration Administration at the end of last year.

The officers conduct thorough inspections of drivers' documents and closely examine every truck, looking for stowaways and illegal goods. "We cannot let our guard down for a second, because we know what we do matters for national security," Wang said.

To support booming cross-border trade, freight and passenger inspections are conducted seven days a week. The port only closes for three days each year, during the Spring Festival Holiday.

"The volume of agricultural produce, such as soybeans, imported from Russia has surged this year. We often work overtime to ensure there is no delay in clearing them for the domestic market," Wang said.

Blagoveshchensk is capital of the Amur Oblast, Russia's key soybean production area, where some Chinese companies have rented land to grow soybeans and ship them back to China.

"The soybean business is booming. We can easily sense the changes in the trade between China and Russia," Wang said.

Meanwhile, after construction of a natural gas pipeline started in June 2015, the number of trucks loaded with machinery rose significantly, he added. The pipeline, which carries natural gas from Russia to Shanghai via Heihe, began operating on Dec 2.

As the existing transportation infrastructure could not support the development of cross-border trade, especially after the introduction of the Belt and Road Initiative, construction of a permanent bridge between Heihe and Blagoveshchensk started in December 2016. The structure was completed in May.

It is the first bridge built over the Heilongjiang River to connect China and Russia. After it opens next year, more than 3 million tons of goods are expected to cross it annually, almost four times the freight volume last year, according to Yu Fei, head of the Heilongjiang Department of Transportation.

The busy cargo ferry port will be quieter once the bridge becomes operational, but bilateral trade will no longer be affected by the condition of the river.

That will pose new challenges for the inspection officers, Wang said.

"By then, more officers will be based at a new cargo inspection facility near the bridge. It will mark a new phase for our work, which will need to be more efficient than ever to cope with the ever-rising freight volume," he added.