At least 13 people were killed and 30 injured in a horrific coach crash on the motorway on Croatia's Adriatic coast early Sunday, police said, issuing a new toll.

"The situation is changing from one moment to the next. The latest toll is 13 dead," police spokeswoman Kristina Maodus said, adding "It's definitely the worst accident that has ever happened in this region of Croatia.

The earlier toll was 10 dead and 30 injured, some of them critical.

Hours after the accident, emergency services were still working to extricate some of the injured passengers, local prosecutor Pavo Rukavina told the Hina national news agency.

"It is horrific. They are trapped, they are crying out in pain," he said.

The accident happened around 6.00 am (0400 GMT) near Zir on the motorway Croatia's Adriatic coast linking the capital Zagreb and the port of Split.

The coach which had Slovak number plates was carrying about 50 passengers, but their nationality was not immediately known, police said.

At least 20 injured people had been taken to hospital in nearby Gospic where three emergency operations were already under way, Rukavina said.

Hina said a helicopter had been sent to the scene to transport the injured to hospital.

The accident apparently happened when the coach clipped a metal safety barrier before hitting the concrete pillar of a viaduct.

Croatian authorities were not immediately able to say whether the passengers on the coach were tourists.

When the tourist season is in full swing, Croatia welcomes more than 10 million visitors -- more than twice the country's population of 4.4 million - particularly to the Adriatic coast.