The number of illegal immigrants crossing into the United States from Mexico declined by 40 percent from January to February, the Department of Homeland Security Secretary said late Wednesday.

The downturn came after President Donald Trump took office on Jan. 20 vowing to deport many of the estimated 11 million illegals in the United States.

The flow of illegal border crossings – measured by apprehensions and the prevention of 'inadmissible persons' apprehended at the southern border by U.S. Customs and Border Protection – dropped to 18,762 in February from 31,578 in January, DHS Secretary John Kelly said in a statement.

He said CBP, which compiled the data, historically sees a 10 percent to 20 percent increase in apprehensions of illegal immigrants from January to February.

Homeland Security Secretary John Kelly said in a statement Wednesday night that the number of people crossing illegally from Mexico to the U.S. dropped sharply last month

This chart from the U.S. Customs and Border Protection agency shows the 40 per cent drop (light blue line, left) that followed President Donald Trump's inauguration

On Jan. 25, Trump ordered the construction of a wall along the roughly 2,000-mile U.S.-Mexico border, moved to strip federal funding from 'sanctuary' states and cities that harbor illegal immigrants, and expanded the force of U.S. immigration agents.

'Since the administration's implementation of Executive Orders to enforce immigration laws, apprehensions and inadmissible activity is trending toward the lowest monthly total in at least the last five years,' Kelly said.

'The drop in apprehensions shows a marked change in trends,' said Kelly. Trump took office January 20.

He stressed that the sharp decline means fewer people are taking the huge risk of putting their fate in the hands of human traffickers.

'Early results show that enforcement matters, deterrence matters, and that comprehensive immigration enforcement can make an impact,' said Kelly, one of Trumps' closest allies on tightening border security and on the president's controversial pledge to build a wall there.

Border Patrol agents had fewer people to arrest in the southwestern U.S. last month

Customers and Border Protection trumpeted the numbers Wednesday night on Twitter

During his campaign, Trump appalled Mexicans and many Americans by referring to Mexicans who crossed the border illegally into the U.S. as drug dealers and criminals.

Hispanics or Latinos are the largest US minority; most U.S. Hispanics are of Mexican descent or immigrants from Mexico.

The decline in illegal border-jumping can be seen in the number of empty beds at Texas immigration detention centers, the San Antonio Express-News reported Wednesday night.

Already this year U.S. immigration officials have shut down emergency processing centers in South Texas and near El Paso, that they opened in December to handle an influx of families.

Immigration and Customs Enforcement reported on Monday that one 830-bed facility held just 194 people. A larger 2,400-bed detention center held 439.

In December so many families were crossing the border illegally that ICE was forced to release hundreds to create bed space for new detainees.

The agency said it's holding so few people because 'fewer apprehensions are being made along the Southern border.'