The coronavirus pandemic "continues to accelerate" across the globe, the World Health Organization (WHO) has warned.
Around the world, more than 640,000 deaths involving coronavirus have been reported to the WHO, its leader Dr Tedros Adhanom Ghebreyesus confirmed, out of almost 16 million cases.
"And the pandemic continues to accelerate," Dr Tedros told a coronavirus media briefing, "in the past six weeks, the total number of cases has roughly doubled."
While European nations - such as Spain, France and Germany - are experiencing fresh spikes of Covid-19, the US, Brazil and other countries are still gripped by their first deadly wave of the virus.
The WHO praised countries such as Germany and South Korea for keeping strict measures - such as mandatory face masks and banning mass gatherings - in place.
“Where these measures are followed, cases go down. Where they are not, cases go up,” Dr Adhanom Ghebreyesus said.
On Friday, Spain's deputy chief of health emergencies María José Sierra admitted she was worried the country could "already" be experiencing its second wave of coronavirus.
WHO emergencies programme head Dr Mike Ryan said rather than countries focusing on whether they are experiencing second waves, they should be dedicated to implementing strict health guidelines.
He acknowledged that countries cannot keep their borders shut forever, but said it is "clear" that "pressure on the virus pushes the numbers down, release that pressure and cases creep back up".
The UK has reacted to spikes in Spain by advising against all but essential travel to the mainland and enforcing a 14-day quarantine on anyone returning from there.
Dr Ryan said travel bans alone are "are not effective in dealing with the movement of disease", adding how they should be used "in conjunction" with other measures to stop the virus spreading.
"The virus is everywhere and the virus will move when it gets the opportunity to move," he told a media briefing, but said it can be restricted with measures including hand washing and face covering.
Countries in Europe are not the only ones experiencing new spikes in cases of coronavirus.
Mainland China is battling a return, as is Hong Kong, Australia, Japan, Vietnam and other countries in Asia.
Australia’s Deputy Chief Medical Officer Michael Kidd said, following a spike in cases, it is inevitable "that there will be many further deaths in the days ahead".
Vietnam is evacuating 80,000 people from the central city of Da Nang after three residents tested positive at the weekend, the government said on Monday.
Dr Tedros said "although our world has changed, the fundamental pillars of the response have not", as he encouraged people to continue following safety measures.
"We are not prisoners of the pandemic. Every single one of us can make a difference", Dr Tedros added, "the future is in our hands".