Tougher lockdown measures are under consideration in Scotland, Nicola Sturgeon has announced, after Covid-19 cases rose by 15% in the past fortnight.

She said the new measures announced on Saturday – cutting festive easing to Christmas Day visits only, a travel ban, the Boxing Day increase in levels and a delay in pupils returning to schools – are needed to counter the risk of “exponential growth” of the new, more infectious variant of the virus.

Speaking at a review of restriction levels at the Scottish Parliament, she said this system has “until now been effective”, but as more information on the new strain emerges consideration will be given on whether the top level – Level 4 – needs to be strengthened.

She said: “It seems that we are facing a virus that spreads much faster now than in March, so we need to consider whether the current Level 4 restrictions will be sufficient to suppress it.”

As part of this, plans to resume in-class teaching for all pupils by January 18 will be kept under review.

Mainland Scotland will be placed into Level 4 on Boxing Day, with the islands moving to Level 3.

As she announced 43 deaths of coronavirus patients and 1,316 new cases of coronavirus in the past 24 hours, the First Minister said when Level 4 comes into force, people should “stay at home as much as possible”, with consideration given on whether this should become law.

Further changes to this level include homeware shop and garden centres being restricted to click and collect opening.

Addressing the rising cases, Ms Sturgeon said: “After a sustained period of decline, our case numbers are now more volatile and have risen by around 15% in the last couple of weeks.

“The numbers of people with Covid who are in hospital and ICU have also risen slightly again after a period of quite marked decline.”

She said analysis suggests in the week beginning December 9 around 14% of positive coronavirus cases in Scotland already had a gene linked to the new variant, up from 5% at the end of November – adding it was “not unreasonable to assume that the proportion may be higher now”.

The First Minister stressed this is “still a significantly lower level than England, where it is thought that the new variant accounts for 36% of cases, and will be even higher in London and the South East”.

Ms Sturgeon said: “The very rapid spread in London and the South East serves as a warning of what we will face here if we do not take firm action to suppress the virus.

“We have a real concern that, without significant counter measures, we could be facing another period of exponential growth as we enter the new year.

“That would mean many more people catching Covid and, even without this new strain causing more severe illness, that would result in many more people needing hospital and intensive care. That would put an enormous strain on the NHS and lead to much more loss of life.

“To be blunt, that is what we have to act now to stop.”

She added: “That is why we announced significant additional measures on Saturday.

“I know how tough these are, but we believe they are essential to avoid an extremely serious deterioration in the situation as we move into the New Year.”

Giving a further update on the daily coronavirus statistics, Ms Sturgeon said the death toll of people who first tested positive for the virus within the previous 28 days is now 4,326.

The daily test positivity rate is 7.5%, up from 6% on Monday and the number of people who have tested positive since the start of the pandemic is 114,366.

There are 1,045 people in hospital confirmed to have the virus, a fall of 33 in 24 hours. Of these patients, 60 are in intensive care, down by one.