Around 190 people have been ordered to undergo mandatory Covid screening on Saturday, after health authorities reported an outbreak at a Yuen Long restaurant.

It came as four customers who visited the Peony Golden Court restaurant on the morning of May 1 had tested positive for the coronavirus.

Albert Au from the Centre for Health Protection said while the four patients were seated at different tables, they were all at the centre of the restaurant.

"We believe that in the course of the meal, probably there was a silent transmitter [who was] asymptomatic that went in the restaurant," Au said.

"The four patients didn't know one another, but they appeared at the same time in the restaurant, so we believe it is likely that these four people were infected in the course of their meal in the restaurant."

Among the four patients was a cleaner who worked at a Pok Oi Hospital care home.

One of the patient's close contact – another care home staff – has since tested positive for the virus, while three other residents there are being quarantined.

Meanwhile, new coronavirus cases in the city dropped slightly to 278.

Au said 18 of the infections were imported, and they are looking into a patient who tested positive 12 days after arriving in Hong Kong.

For the first time in almost three months, health officials have recorded no additional Covid-related deaths.