SHANGHAI (BLOOMBERG) - Shanghai said it plans to achieve "no community spread" of the virus by mid-May, a crucial milestone that has eluded the city despite strict lockdown measures that have now stretched to nearly six weeks.

The city will implement "orderly opening-up, limited movement, effective control and classified management" after achieving no community spread, said vice mayor Wu Qing at a Friday (May 13) briefing.

It's the first time city officials have publicly set a timeline to reach the goal, which China sees as a pre-requisite before restrictions can be eased.

Officials define "no community spread" as three consecutive days of zero cases found outside of those already in quarantine. While Shanghai has sporadically reported days with zero cases found outside of quarantine, it has yet to be able to sustain a three-day stretch.

On Friday, the city reported four cases found in the community for Thursday, up from two the day before.

Halting community spread would embolden officials to start lifting restrictions under a lockdown and allow factories to resume production. Southern tech hub Shenzhen and northeastern province Jilin also began rolling back curbs and restart manufacturing after a similar containment milestone was achieved.

The lockdown imposed on Shanghai's 25 million residents has been one of the longest since the experience of Wuhan, where the pathogen was first detected in late 2019.

The city's crisis has prompted other places in China to enact hardline measures at the merest sign of Covid-19 flareups to avoid the social and economic dislocation endured by the financial hub.