All FairPrice stores will stay open "come what may", said FairPrice group chief executive Seah Kian Peng, stressing that there was no need to rush to supermarkets to stock up on food.

"My colleagues are doing our best," he wrote in a Facebook post, responding to a surge in buying at supermarkets.

"Our stores will remain open today, this weekend, next week, and so no need to worry that we will not be functioning."

Yesterday, Prime Minister Lee Hsien Loong announced that all workplaces will close from Tuesday, except for those that provide essential services or are considered to be in key economic sectors.

These include food establishments, markets and supermarkets, as well as clinics, hospitals, utilities, transport and key banking services.

But long queues formed at supermarkets all over Singapore even before the announcements, driven by speculation that strict movement restrictions were imminent.

Mr Seah said that when stores see 50 per cent more customers who buy 150 per cent of their normal purchases, this is equivalent to a 225 per cent increase.

"This adds strain to the entire system and you can expect empty shelves till more stocks are delivered from our warehouses to the stores and also replenished at the store shelves," he added. "So please be patient, buy sensibly and also practise safe distancing."

Mr Seah added that FairPrice is getting more manpower for crowd control and to help existing staff. He encouraged customers to look out for one another in stores and help those who are more vulnerable.

"Together, we can overcome and together we will," he said.

In a separate post, Trade and Industry Minister Chan Chun Sing stressed that Singapore's food supply lines are intact.

He urged Singaporeans to purchase in a responsible manner, adding: "Please spare a thought for the more vulnerable amongst us and remember that our individual actions will have a ripple effect on the rest of society. Panic buying will disrupt our supply lines and allow profiteers to take advantage of us."