Smugglers disguised $5 million worth of methamphetamine as watermelons and tried to truck them across the border from Mexico, US border agents said.

More than 4,500 pounds (2,000 kilograms) of the addictive drug were wrapped in paper packages painted to look like the juicy fruit and hidden amongst other cargo.

Border agents pulled over the produce-laden tractor-trailer at Otay Mesa in California on Friday and got in amongst the cargo for a closer look.

There they discovered more than 1,200 watermelons were actually bundles of the synthetic drug wrapped in colored paper, US Customs and Border Protection said this week.