Routine mass PCR testing is one of the key tools used to trace outbreaks, with cities such as Beijing and Shanghai requiring residents to show 72-hour test results to enter public spaces and use public transport.

Economically vital cities, including the Chinese capital Beijing, have jumped on the rising infections, demanding more PCR tests for residents and locking down neighbourhoods and even districts in some cases.

The launch came two days after South Korea and US forces launched their military exercise in the waters off South Korea's east coast involving an aircraft carrier.

Proof of a negative PCR test once every few days is required to guarantee access to public venues, places of work and mass transit - even when there is no outbreak.

The isolated, nuclear-armed North has conducted missile tests at an unprecedented pace this year.

Shanghai officials say seven of the city's 16 districts will carry out PCR testing for all residents over the weekend due to the discovery of a few cases in the community, saying they want to prevent a renewed outbreak.

The missile flew 470km and reached an altitude of 780km, Seoul's Joint Chiefs of Staff says, adding it is a 'blatant violation of UN Security Council resolutions'.

While only the authorities working together with independent parties and the scientific community can verify these probabilities, so far we have no reason to assume the worst.