A major earthquake of magnitude 6.3 hit Croatia, killing five people - including a 12-year-old girl - and causing widespread damage in a town near the capital Zagreb.

Firefighters rescued a man and a boy trapped in a car buried in rubble in Petrinja after buildings collapsed, leaving the streets littered with fallen bricks and dust.

At least 20 people were hospitalised with injuries, two with serious ones, according to officials. Five deaths including the girl were reported by state broadcaster HRT TV.

"My town has been completely destroyed, we have dead children," mayor Darinko Dumbovic said in a statement to HRT.

"This is like Hiroshima - half of the city no longer exists. The city has been demolished, the city is no longer liveable. We need help."

The Croatian military was deployed in Petrinja to help with the rescue operation and the Croatian Red Cross described the situation as “very serious” as it despatched crisis teams to the area.

Prime minister Andrej Plenkovic travelled to the town to oversee the efforts to accommodate homeless residents in local hotels and army barracks after what he described as a "devastating earthquake which was felt in many parts of Croatia.”

He tweeted: “We mobilized all available services to help people and clear the destroyed parts. The most important thing now is to save human lives.”

The European Mediterranean Seismological Centre said the quake centred 51km southeast of Zagreb was the largest to hit Croatia this year and the 14th felt in the area in the last 31 hours including a 5.2-magnitude tremor on Monday.

Tomislav Fabijanic, head of emergency medical service in Sisak, a city close to Petrinja, said there were many injured in the region.

"There are fractures, there are concussions and some had to be operated on," he said.

In Zagreb, people ran out into the streets and parks in fear and there were reports of several leaving the city despite a ban on travel due to the coronavirus outbreak. The tremor was also felt in neighbouring Bosnia and Serbia, and Slovenia's STA news agency said that the country's sole nuclear power plant was shut down as a precaution.

In March, an earthquake of magnitude 5.3 hit Zagreb causing one death and injuring 27 people. That was said to be the biggest tremor to hit Zagreb in 140 years.

European Council president said the EU was offering its “full support and assistance”. He tweeted: "We are closely following the situation in Zagreb following the devastating earthquake.

“Our thoughts go out to the injured and frontline workers.”

Additional reporting by agencies