Rooms of the athletes and physical trainer Christopher Xuereb were searched and drugs and supplements were seized, Udine police captain Antonio Pisapia told The Associated Press.
Pisapia said it was unclear if the substances were illegal, and that they were being analyzed.
"We are examining the substances now," Pisapia said. "No arrests have been made and nobody has been placed under investigation."
The raid took place at the Fra i Pini hotel in Lignano Sabbiadoro in northeastern Italy.
Powell, a former world-record holder at 100 metres, and Simpson tested positive for the stimulant oxilofrine at the Jamaican championships last month, their agent said Sunday.
The police captain with the specialized NAS unit added that Powell and Simpson were informed of the positive tests Saturday morning.
The raid came in stark contrast to the warm reception that the runners generally receive in Lignano, and the town's mayor, Luca Fanotto, recommended "caution" before drawing conclusions.
"The Jamaican team has chosen the sports facilities of Lignano Sabbiadoro as their training base for years and they never forget to thank the city from podiums all over the world," Fanotto said in a statement.
A local meet is scheduled for Tuesday in Lignano, and the Jamaicans had been scheduled to compete as they do most years. But neither Powell or Simpson was on start lists released Monday.
The news of the positive tests for Powell and Simpson came the same day that American 100-metre record holder Tyson Gay revealed that he also failed a doping test.
Powell was the last man to hold the 100-metre world record before Usain Bolt broke it in 2008. He also helped the Jamaicans to the 400-metre relay gold medal at the 2008 Olympics.
Simpson won Olympic gold in the women's 400 relay in 2004 and silver in 2012, along with an individual silver in the 100 in 2008.
The doping positives come a month after another Jamaican Olympic champion, Veronica Campbell-Brown, tested positive for a banned diuretic.Suggest a correction