Financial adviser Jane Neoh has been trying to buy groceries online almost every day for the past few weeks without success.
"I've tried buying some vegetables, meat and household items from FairPrice and RedMart (online) but haven't been able to get any delivery slots so far," she said, adding she is grateful to still be able to go to supermarkets for the goods.
The 32-year-old said: "I want to avoid the crowds so I go to the 24-hour supermarkets around midnight or 1am."
Like Ms Neoh, many shoppers have found online grocery shopping almost impossible in recent weeks.
Demand has risen tremendously due to the coronavirus outbreak and spiked again this past weekend when safe distancing measures came into play, with the Government calling for people to stay home and shop online.
A check with various online grocery shopping services yesterday afternoon, including FairPrice, Cold Storage and Giant, showed that all delivery slots had been taken up.
A spokesman for Dairy Farm, which runs Cold Storage and Giant, said staff are working round the clock to fulfil all pending orders.
She said: "We have since added extra picking and delivery capacity to cope with the increase in demand, with new delivery slots being added daily."
She added: "Please do not panic buy and do not try to stock up with overly large quantities of daily essentials."
Chief executive of Lazada Singapore James Chang said staff have been "working tirelessly" at the company's e-grocer RedMart to manage the rise in demand.
Yesterday, RedMart started prioritising the sale of daily essentials such as milk powder and rice and made changes to its logistics to cater to the rising demand.
Among other measures, the online supermarket is limiting orders to 35 items and reducing its range of goods to focus on daily essentials.
In a letter sent to customers yesterday, the e-grocer said the new updates would help "ensure that delivery slots remain available and consumers can receive their essentials in a timely manner".
Mr Chang said: "We do hope to serve a larger community now, and our data shows that consumers are buying essentials, such as rice, eggs and milk powder, so we're making timely changes on our system to cater to this precise demand at this time."
As part of the new measures, delivery slots will now be assigned based on address and will be temporarily limited to specific days and times for each address.
The e-grocer will move from delivering to locations across Singapore to focusing on one area each day. This will help to optimise manpower and available delivery vehicles, it said.
Mr Chang said: "This change will help us in maximising our logistics, and allow each household to order twice a week."
On Sunday, Transport Minister Khaw Boon Wan said taxi and private-hire car drivers can now also deliver groceries. But transport companies say operational details are still unclear.
Ms Tammy Tan, group chief corporate communications officer at ComfortDelGro, said: "We are currently working out operational details with a few companies for the delivery of food and groceries and will keep our drivers posted once these have been sorted out."
SMRT Roads senior vice-president Tony Heng said: "We welcome the good news for SMRT's taxi partners, as we have been exploring various ways to increase the number of trips for them during this challenging time."