Donald Trump has called for drug dealers to face the death penalty in a bid to tackle the opioid epidemic ravaging the United States.

In a speech on Sunday (AEST), Mr Trump argued America should adopt similar drug policies to those in Singapore, where he claimed there was “no problem”.

The President, who announced a 90-day public health emergency in October, said he had been impressed by the Asian nation’s approach during discussions with Singaporean officials.

“These guys don’t play games,” Mr Trump told a rally in Pennsylvania.

“I said, ‘How are you doing on drugs?’ ‘No problem’. I said, ‘What do you mean no problem?’ ‘That means if we catch a drug dealer, death penalty’.

“And they don’t have a problem.”

Mr Trump argued that in the US, people convicted of murder often received a life sentence or the death penalty, but drug dealers did not, despite killing “thousands of people”.

“I don’t know if you’re ready. I don’t know if this country’s ready for it, but I think … it’s a discussion we have to start thinking about.”

Though Mr Trump’s remarks on Sunday were not scripted, he also suggested executing drug dealers earlier in the month.

And the Trump administration is said to be examining policy changes that would allow prosecutors to seek the death penalty, according to The Washington Post.

Last year, a United Nations study found the US led the world for drug overdose deaths. It had 27 per cent of all fatalities, but only 4 per cent of the world population.

Meanwhile, a third of all drug overdose victims in 2016 had taken synthetic opioids like fentanyl, according to the National Institute for Drug Abuse.

Singapore has among the lowest rates of drug abuse in the world, but its drug policies are often described by critics as draconian.

The country imposes a mandatory death penalty on a person carrying a specified quantity – for example at least 500 grams of cannabis, 30 grams of cocaine or 250 grams of methamphetamine.

The burden of proof also falls on the defendant, rather than the authorities.

It means anyone who owns a car or house where drugs are found is presumed to have possessed them, while a person can also be arrested merely for being in the presence of drug users.

Critics of Mr Trump’s call have suggested capital punishment could drive drug users further underground and could lead to fewer people seeking treatment.

Public health experts have urged the government to provide more funding for cash-strapped treatment centres in the worst-hit states, such as West Virginia.

The President has previously praised Philippines leader Rodrigo Duterte, whose hardline stance on drugs includes encouraging vigilante killings of suspected drug dealers and addicts, a bounty system and a shoot-to-kill policy for police.

Mr Trump made the death penalty call during a free-wheeling speech at a rally in Pennsylvania to support a Republican candidate for Congress.

He used the address to unveil his 2020 campaign slogan, “Keep America Great!”, and suggested he would “love to run against Oprah”, claiming he knows “her weakness”.

After confirming last week that he would meet with North Korean leader Kim Jong-un, a first for a US president, Mr Trump said on Sunday he could quickly walk away if a breakthrough appeared unlikely.

“Who knows what’s going to happen?” he said.

“I may leave fast or we may sit down and make the greatest deal for the world.”

He also threatened to impose taxes on German automakers Mercedes-Benz and BMW after the European Union threatened to appeal the Trump administration’s steel and aluminium tariffs at the World Trade Organisation.

Mr Trump said on Saturday that Australia would be exempt from the tariffs.