Chinese officials admitted Wednesday they have faced challenges getting enough supplies to residents in locked-down Xi'an, after the city's inhabitants took to social media to complain they didn't have enough food and call for help.

Thirteen million residents in northern Xi'an are in their seventh day of home confinement, and national health officials have called for measures to be strengthened further as China battles its worst virus surge in months.

Beijing has followed a strict "zero Covid" strategy involving tight border restrictions and targeted lockdowns since the virus first surfaced in a central city in late 2019.

But officials admitted at a press conference Wednesday that "low staff attendance and difficulties in logistics and distribution" had led to trouble providing essential supplies as the country faces a resurgence in infections.

A day before, many residents asked on social media for help acquiring food and other essentials, with some saying their housing compounds would not let them out even though they were running out of food.

Xi'an official Chen Jianfeng told reporters that the local government has mobilised enterprises to step up community distribution, with cadres supervising wholesale markets and supermarkets.

"We're trying our best to assist in the problem of staff turnout, and are issuing passes for vehicles that guarantee the supply of necessities," he said.

But some were still struggling with supplies.

Thirteen million residents in northern Xi'an are in their seventh day of home confinement
Thirteen million residents in northern Xi'an are in their seventh day of home confinement AFP / STR

"How do we live? What do we eat?" one user wrote on the Twitter-like Weibo platform.

"Days ago, we could go out once to buy groceries but that's been cancelled... all online grocery apps are either sold out or beyond the delivery range," the user added.

The city stepped up confinement measures on Monday, with many residents told not to leave their homes except for virus testing -- after previously being told they could go out once every three days to buy supplies.

Authorities had previously insisted that supplies remain stable as they maintain strict controls of movement into and out of Xi'an.

The city has logged over 960 domestic virus cases since December 9.

Although the surge in China is low in comparison to rampant cases in Europe and the United States, Chinese officials imposed what they have called the "strictest" possible curbs in Xi'an.

Authorities have also detained at least seven people in the city over attempting to skip quarantine, disrupting order and spreading rumours, local media said.

The outbreak comes as Beijing prepares to welcome thousands of overseas visitors to February's Winter Olympics.