After three years, the mainland is opening its border with Hong Kong and ending a requirement for incoming travellers to quarantine, dismantling a final pillar of a zero-COVID policy that had shielded China's people from the virus but also cut them off from the rest of the world.

“I'm so happy, so happy, so excited. I haven't seen my parents for many years," said Hong Kong resident Teresa Chow as she and dozens of other travellers prepared to cross into mainland China from Hong Kong's Lok Ma Chau checkpoint early on Sunday.

"My parents are not in good health, and I couldn't go back to see them even when they had colon cancer, so I'm really happy to go back and see them now," she said, adding that she plans to head to her hometown in eastern China's Ningbo city.

On a visit to the station, Chief Executive John Lee Ka-chiu said the sides would continue to expand the number of crossing points from the current seven to the full 14.

“The goal is to get back as quickly as possible to the pre-epidemic normal life," Lee said. “We want to get cooperation between the two sides back on track."

At Hong Kong's Lok Ma Chau checkpoint, a driver who only gave his surname Yip, said he was among those who could not wait to travel to the mainland.

"It's been three years, we have no time to delay," he said.

Up to 50,000 Hong Kong residents are now able to cross the border daily at three land checkpoints after registering online. Another 10,000 are allowed to enter by sea, air or bridges without needing to register in advance

Tan Luming, a port official in Shenzhen on the border with Hong Kong, saying about 200 passengers were expected to take the ferry to Hong Kong, while another 700 were due to travel in the other direction, on the first day of reopening.

Tan said a steady increase in passenger numbers is expected over coming days.

At the Beijing Capital International Airport, barriers that once kept international and domestic arrivals apart were gone, as were the "big whites" -- staff in hazmat suits long a fixture of life in zero-Covid China.

Families and friends exchanged emotional hugs and greetings with passengers arriving from Hong Kong, Warsaw and Frankfurt at the airport's terminal 3, meetings at the arrival hall that would have been impossible just a day ago due to a now cancelled requirement for travellers from abroad to quarantine.

“I've been looking forward to the reopening for a long time. Finally we are reconnected with the world. I'm thrilled, I can't believe it's happening,” said a business woman surnamed Shen, 55, who flew in from Hong Kong.

Investors hope the reopening will eventually reinvigorate a $17-trillion economy suffering its lowest growth in nearly half a century. But the abrupt policy reversal has triggered a massive wave of infections that is overwhelming some hospitals and causing business disruptions.

The border opening follows Saturday's start of "chunyun", the first 40-day period of Lunar New Year travel, which before the pandemic was the world's largest annual migration of people returning to their hometowns of taking holidays with family.

Some 2 billion trips are expected to be made this season, nearly double last year's movement and recovering to 70% of 2019 levels, the government says.

China on Sunday also resumed issuing passports and travel visas for mainland residents, and ordinary visas and residence permits for foreigners.

Beijing has quotas on the number of people who can travel between Hong Kong and China each day.