British Prime Minister David Cameron on Thursday described migrants trying to reach Britain as a "swarm," triggering criticisms from political opponents for his use of "dehumanizing" language over the ongoing migrant crisis.

Thousands of migrants have gathered in the northern French port city of Calais trying to reach Britain through the Channel Tunnel, leading to strengthened security measures by British and French authorities in their border area.

When asked about the crisis on Thursday, Cameron described the migrants as "a swarm of people coming across the Mediterranean, seeking a better life, wanting to come to Britain."

The remarks drew criticisms from politicians of the opposition Labour Party, who questioned the appropriateness of the prime minister's language.

"He should remember he's talking about people and not insects and I think it's a very worrying turn that he appears wanting to be divisive and whip people up against the migrants in Calais," the Labour Party's acting leader Harriet Harman said on national TV.

Urging Cameron to get the situation sorted out with the French, Harman warned that "just sounding off against people describing them as a swarm is not the way to solve the problem."

"All of these people need to be assessed as to whether they're genuine refugees in which case they should be granted asylum, or they're not in which case they should be deported," she added.

Leader of the Liberal Democrats Tim Farron also accused Cameron of "dehumanizing migrants."

"By blaming 'migrant swarms' for the current crisis in Calais, David Cameron risks dehumanizing some of the world's most desperate people. We are talking about human beings here, not insects," Farron said in a statement.

"This means as a country we should accept our fair share of refugees by signing up to the EU asylum policy, rather than expecting others to do it for us. If Ireland can sign up to the scheme, why can't we?" he added.

"By using the prime minister's language we lose sight of how desperate someone has to be to cling to the bottom of a lorry or train for the chance of a better life," Farron continued.

A Sudanese national died Tuesday when about 1,500 migrants tried to make their way to the Eurotunnel platforms in Calais.

Britain has deployed additional border force staff and sniffer dogs in northern France and bolstered screening checks at Dover for both tourist and freight vehicles to ease the migrant pressure.

The country has also agreed to provide additional funding of up to 7 million pounds (10.9 million U.S. dollars) to increase security at the Channel Tunnel railhead at French town Coquelles.

"Law and order in and around Calais is the responsibility of the French authorities, but the UK continues to work with its French counterparts to strengthen the security of the border to stop migrants entering the UK illegally," Downing Street said in a statement.