No "significant easing" of Wales' Covid restrictions should be expected when the current guidelines are reviewed this month, the health minister said.
Vaughan Gething said it was "good news" that case rates were falling, but warned they still remained high.
He told a Welsh Government briefing the NHS remained "under pressure" with critical care services operating at 150% of capacity.
A further 44 people have died with coronavirus, taking the total to 4,346.
And another 13,800 people had their first vaccine in the past day in Wales, taking the total to 175,816, according to latest figures.
Mr Gething made the comments as he was outlining the current situation with Covid in Wales, but he said he did not want to prejudge a Welsh Government decision on the review.
Wales has been in a level four lockdown since before Christmas with a decision on a review of the current restrictions expected by 29 January.
The seven-day rolling case rate for Wales is 285 cases per 100,000 people, which is down from a high of 636 on 17 December.
A key indicator in deciding to put Wales into the strictest alert level was Covid rates exceeding more than 300 cases per 100,000 people in a seven-day period.
Wrexham has the highest rate in Wales with 673 cases per 100,000 people, followed by Flintshire with 480.5.
Mr Gething said: "If we come out of level four too soon, too fast, we could well see a rebound in Covid rates.
"And we could end up doing something that overwhelms our health service with all the harm that would cause to our staff and people who need our health service.
"People shouldn't expect any significant easing at the end of this current phase."
He said the Welsh Government would make a decision following advice from its scientific advisers and the chief medical officer.
Under current lockdown rules, people are required to make essential journeys only and schools have been closed to most pupils with online learning in place.
What's the situation in hospitals?
- The number of Covid patients in hospital on 19 January was 2,700, down from a record high last week
- Numbers have risen in Cardiff and Vale by 10%, but fallen elsewhere
- Aneurin Bevan health board currently has the most Covid patients - 613 - and nearly half of all its patients have the virus or are recovering from it
- All south Wales health boards have more than 40% of patients in hospital beds with Covid
'More difficult choices'
Mr Gething also said there would be a "great many more difficult choices to make" on dealing with Covid-19 with the Senedd election due in May.
Ministers are seeking Senedd members' support for emergency legislation to allow the poll to be delayed by up to six months as a last resort.
Mr Gething told the briefing: "Even by the first week of May we can be confident that there will still be a great many more difficult choices to make before we can say the pandemic is over, and before we're then into what I believe will be a full term of recovery from the economic crisis that Covid has caused, as well as the health crisis.
"This is a piece of legislation to guard against the possibility that Covid rates are so significant that we can't have an election."