Slovak Prime Minister Robert Fico is now out of immediate danger but still in a serious condition, according to his deputy on Sunday, four days after an assassination attempt that sent shockwaves through Europe.

"We are all a little calmer," Deputy Prime Minister Robert Kalinak told a news conference outside the hospital where Fico is being treated in the central Slovak town of Banska Bystrica.

The prime minister, 59, was hit by four bullets on Wednesday in an attack that raised alarm over the polarised state of politics in the central European country of 5.4 million people.

Kalinak told journalists that Fico's condition was still too serious to consider transferring him to the hospital in the capital. But the worst fears had passed for now.

"When we were saying that we want to get closer to a positive prognosis, then I believe that we are a step closer to that," he added.

"The prime minister has stepped away from his life being in danger, but his condition remains serious and requires intensive care."

The shooting was the first major assassination attempt on a European political leader for more than 20 years and has drawn international condemnation.

Political analysts and lawmakers say it has exposed an increasingly febrile and polarised political climate both in Slovakia and across Europe.

The Slovak Specialized Criminal Court ruled Saturday that the suspect, identified by prosecutors as Juraj C., would remain in custody after being charged with attempted murder.

Local news media say the suspect is a 71-year-old former security guard at a shopping mall and the author of three collections of poetry.