Not all migrant workers cleared of Covid-19 will be able to return to work immediately.

National Development Minister Lawrence Wong said yesterday that some projects require staff from different firms to work together, but if some of those employees are not yet cleared, the entire operation can be held up.

Employers and contractors will also have to fulfil safety requirements before staff can start work.

Mr Wong, who co-chairs the Covid-19 task force, was responding to a question at a virtual press conference about how many foreign workers are back on the job.

He said that "easily more than 80 per cent" of the migrant workers living in dormitories have been cleared so far, but there will be a time lag before they resume work.

He cited the example of a construction project that often involves multiple contractors.

"If the project is at a particular stage of work and you need workers... with the skill sets... for that particular stage of work, but the subcontractor with the workers is not able to restart... then the entire project is stalled for the time being.

"And that is why you do see often the workers may be cleared but they may not all be working immediately."

Mr Wong said agencies like the Building and Construction Authority and the Economic Development Board are working with firms that have not yet met safe management measures, including issues related to work sites and accommodation.

He told employers of foreign workers: "Do not wait until middle of August when all the workers are cleared.

"Submit all the requirements now so that you can get all of these working in parallel, and then when the workers are ready, you can immediately have work resume as soon as possible."