Singer machines were reported to be changing hands for exorbitant prices
Saudi police say they are investigating a hoax that has seen people rushing to buy old-fashioned sewing machines for up to $50,000 (£33,500).
The Singer sewing machines are said to contain traces of red mercury, a substance that may not exist.
But it is widely thought that it can be used to find treasure, ward off evil spirits or even make nuclear bombs.
It is believed that tiny amounts can sell for millions of dollars, the Saudi Gazette reported.
The paper said that trade in the sewing machines was brisk across the country.
Rumours about the sewing machines have been spreading for days by word of mouth and over the internet, it said.
These included rumours that foreign experts and companies had been buying up Singers.
In Dhulum, it was reported that people had broken into two tailors' shops to steal the machines.
In the city of Madina, people were holding mobile phones up to the machines, due to the belief that they could be used to detect the presence of red mercury.
An interior ministry spokesman said authorities were trying to discover who had spread the rumours.
"We have to find out who started this hoax," he told Reuters news agency.
"People hope to make profit," he added. "This is no different to cases of citizens who put their money in untrustworthy schemes."