Media playback is unsupported on your device Media caption "We're going to spend a lot of time, a lot of effort and a lot of money on the opioid crisis"

The crisis over the US addiction to painkillers - opioids - is a national emergency, says President Donald Trump.

"It's an emergency, it's a national emergency. We are going to spend a lot of time, a lot of effort and a lot of money on the opioid crisis," he said.

The number of deaths from the drugs - prescribed to a third of Americans in 2015 - has quadrupled in 20 years.

Declaring a national emergency means the issue can get prioritised funding and resources from Washington.

"There's never been what's happened to this country over the last four or five years," said President Trump.

Mr Trump spoke to reporters on Thursday from his golf resort in New Jersey, where he has been taking a 17-day "working vacation".

The declaration came in response to a reporter's question, and was not announced through an official White House press release or statement.

Media playback is unsupported on your device Media caption The heroin-ravaged city fighting back

On Tuesday during a meeting at his golf course to discuss the opioid crisis, Mr Trump took a moment to threaten North Korea with "fire and fury" if it continued to engage in provocative nuclear behaviour.

Opioids, according to the US National Institute of Drug Abuse, include the illegal drug heroin, synthetic medications such as fentanyl, or pain relievers that are available by prescription, such as oxycodone, morphine, codeine, and many others.

Many of the victims of drug addiction were initially prescribed legal drugs by doctors to combat pain, but then later switched to the illegal version after their prescription expired.

Patients who are no longer receiving opioids as medication sometimes turn to street drugs such as heroin, which in many cities is cheaper than beer.

Media playback is unsupported on your device Media caption Nashville mayor talks about son's drug overdose

Mr Trump had previously been urged by the White House Commission on Combating Drug Addiction and the Opioid Crisis to declare the emergency.

The commission said this would "awaken every American to this simple fact: if this scourge has not found you or your family yet, without bold action by everyone, it soon will".

New Jersey Governor Chris Christie, who chairs the commission created by Mr Trump, applauded the announcement, saying the group looks forward "to working with this President to address the approximately 142 deaths a day from drug overdoses in the United States".

But on Tuesday, Health Secretary Tom Price suggested that Mr Trump already had the necessary authority to tackle the crisis.

"We believe at this point that the resources that we need or the focus that we need to bring to bear to the opioid crisis at this point can be addressed without the declaration of an emergency," he said.

Mr Trump campaigned partly on a promise to tackle the drug epidemic which has claimed lives in urban, suburban and rural America.

Last week transcripts revealed that Mr Trump referred to the state of New Hampshire, where he campaigned often, as drug-infested.

"I won New Hampshire because New Hampshire is a drug-infested den," Mr Trump told the president of Mexico, according to a leaked transcript of the January phone call.

More on the US drugs crisis

Media playback is unsupported on your device Media caption America's new generation of addicts

As an open-air heroin camp is closed, options narrow