David Cameron has been criticised for describing migrants as a "swarm" trying to get into Britain.
The Prime Minister used the term as the crisis at Calais continued, with large numbers of migrants trying to reach the UK through the Channel Tunnel.
Thousands have attempted to make the perilous crossing, which this week led to a man being killed.
It brings the number of people to have died so far this month to nine, according to Eurotunnel.
The mounting problem has caused travel chaos on either side of the Channel and led to calls for the Army to be sent in to tackle the emergency.
Speaking on his tour of South East Asia, Mr Cameron said: "Look this is very testing.
"I accept that because you've got a swarm of people coming across the Mediterranean seeking a better life, wanting to come to Britain because Britain has got jobs and got a growing economy.
"It's an incredible place to live but we need to protect our borders by working hand in glove with our neighbours the French and that's exactly what we're doing."
But his comments sparked immediate condemnation.
Acting Labour leader Harriet Harman said: "He should remember he is talking about people not insects and I don't think it's going to distract attention for him to just be trying to whip up hostility to those migrants in Calais when he should be sorting the situation out.
"He has been being warned for months, we've been warning him for months."
And in a Twitter post, Labour leadership candidate Andy Burnham said: "Cameron calling Calais migrants a 'swarm' is nothing short of disgraceful."
The Refugee Council described Mr Cameron's remark as "awful, dehumanising language from a world leader."
Meanwhile, UKIP leader Nigel Farage suggested the Islamic State terror group could use the Calais crisis to smuggle militants into the country.
Describing it as a "desperately serious situation", Mr Farage said: "When Islamic State said they will use the tide of people across the Mediterranean to flood Europe with their own jihadist people, shouldn't we take that seriously?
"Because at the moment, not one person is either being checked or processed in either Greece or Italy.
"I would suggest that there's potentially a very serious security dimension to this problem."
Meanwhile, an Egyptian man is reported to have suffered serious burns after hitting an overhead power line as he attempted to get on to the roof of a Eurostar train in Paris.