By Sophie Yu and Josh Smith

BEIJING/SEOUL (Reuters) -An Air Koryo flight from Pyongyang landed in Beijing early on Tuesday for the first time since the COVID-19 pandemic lockdowns began in 2020, as North Korea cracks open its border to some passenger travel.

The flight, JS151, arrived at 9:17 a.m. (0117 GMT), shortly ahead of its scheduled time. It wasn't immediately clear who was aboard, but Western tour companies that operated in North Korea said it appeared to be a special flight that would on the return carry back North Koreans who had been trapped in China by the years of border closures.

The flight comes amid a slow reopening for one of the world's most politically and economically isolated countries.

Cargo train and ship traffic has slowly increased over the past year, but North Korea has only just begun to allow some international passenger travel.

In a first since before the pandemic, Chinese and Russian government delegations flew to Pyongyang last month and last week buses carrying North Korean athletes to a taekwondo tournament in Kazakhstan crossed the border into China.

Photos by South Korea's Yonhap news agency showed lines of people checking in for the return flight to Pyongyang from Beijing with large piles of wrapped boxes and luggage.

Air Koryo has also scheduled flights to Vladivostok on Friday, a diplomat told Reuters, in what would be its first flights to Russia since the pandemic.

"This flight isn’t a full resumption of the route yet, it is a special flight for Koreans only to take people home again after years being stuck overseas," said Simon Cockerell, general manager at Beijing-based Koryo Tours. "The same as the flights that seem likely to happen soon from Vladivostok."

"It’s all happening, but for Koreans first, the rest of us…later," he said.

'GRADUAL OPENING'

North Korean leader Kim Jong Un has built hundreds of kilometres (miles) of new or upgraded border fences, walls and guard posts since the pandemic began, enabling his government to tighten the flow of information and goods into the country, keep foreign elements out and its people in.

Before the pandemic, Russia and China were estimated to host nearly 20,000 North Koreans each, according to a report by the Association of Asian Studies. Since the end of 2019, U.N. Security Council resolutions have required that all countries deport North Korean workers.

It is unclear how many from the North Korean community - mostly students and people who work in restaurants and government-related jobs in areas such as tourism and cultural promotion - still remain in China.

The travel curb hurt not just ordinary people but diplomats as well. The current Chinese ambassador to North Korea, Wang Yajun, had to wait 15 months after being named for the job before he could enter the country this March to take up his role.

Many foreign delegations closed their embassies in Pyongyang because they were unable to rotate staff or ship in supplies for much of the pandemic.

One diplomat for a Western country that pulled its staff from its embassy in Pyongyang said there was no official word from North Korean officials on when they could return.

"We expect a gradual opening with 'friendly' countries first, so we may be a bit down the list," the diplomat said, speaking on condition of anonymity to discuss the sensitive issue.

The Chinese foreign ministry said on Monday that Beijing had approved North Korea's state carrier Air Koryo resuming flights to China.

The Civil Aviation Administration of China did not immediately respond to a request for comment on the future frequency of Air Koryo flights to China and when Chinese state carrier Air China may resume flying its North Korea-China routes.

(Reporting by Sophie Yu, Brenda Goh, Laurie Chen, and Yew Lun Tian in Beijing, and Josh Smith in Seoul; Writing by Josh Smith; Editing by Jacqueline Wong and Raju Gopalakrishnan)