The bureau made the announcement on Friday evening, saying the government is deeply concerned about the two imported cases involving locally based cargo crew.

They also had a meeting with the airline concerned regarding the two cases, and directed the airline to expedite its investigation, submit reports and take follow-up action.

They added they have reviewed and considered enhancements on all possible fronts, and has requested airlines to impose more stringent anti-pandemic rules.

Apart from the daily post-arrival testing and the booster jab mandate, airlines are requested to assign on-site personnel to monitor cargo crew layovers at outports and step up independent auditing.

It is to ensure crew members' compliance with the requirements under closed-loop operation and to minimize their infection risks, the bureau said.

The bureau also requested airlines to impose more stringent restrictions on local cargo crew's movements during their medical surveillance periods, promulgates clearer guidelines and strengthens monitoring, with a view to minimizing their contact with the local community.

Health authorities reported five imported cases on Wednesday, involving three air crew members. Among them, two pilots, aged 57 and 29, were infected with the more infectious Delta+ mutant strain, they said on Thursday night.