Four people were killed and 28 injured, including eight seriously, when a hot air balloon crashed and caught fire early Thursday south of Ljubljana, authorities said.

There was no information about the dead but the injured included two British citizens and two Italians, "all of whom have been hospitalised," police spokeswoman Maja Adlesic told AFP.

She gave no details about their identity or their condition.

The hospital had earlier talked of three Italians and one Briton among the injured.

The accident occurred at around 8:00 am local time (0600 GMT) some 12 kilometres (7.5 miles) south of Ljubljana, a spokesman for the country's civil protection and disaster relief administration said.

He added the balloon was carrying 30 passengers along with the pilot and co-pilot.

"The first doctor who arrived at the accident site confirmed he found four charred bodies," he was quoted as saying by the Slovenian news agency STA in Ig, near the accident site.

Adlesic said three of the balloon's 32 passengers were children, after police had earlier said six children were on board. It was unclear whether any had been killed.

The news website 24ur said a 10-year-old child was in intensive care.

At a news conference, the Ljubljana Clinical Centre confirmed that 21 passengers had been hospitalised there, of whom "eight remain in critical condition."

"Those hospitalised are aged between 10 and 60 years old, some of them are foreigners," the hospital said.

Five injured were admitted to another hospital in Novo Mesto, southeast of Ljubljana, while one person was hospitalised each in Celje and in Jesenice, according to STA.

"The injured passengers were taken to various hospitals so we do not have all the information yet," Adlesic told AFP.

STA reported that the hot-air balloon burst into flames after it was caught in a storm. Another balloon that was in the air at the same time was able to land safely further away.

"There was a storm raging at the time of the accident. The balloons tried to land but were thrown about by turbulence. That's when one of them caught fire," one witness was quoted as saying by the web portal siol.net.

One of the passengers who was lightly injured in the accident, Tomaz Simnec, meanwhile told 24 ur: "The landing was too fast, we hit the ground, rebounded, and then hit the ground again. During the second 'landing' five of us fell out of the basket."

He added that he lost consciousness after falling out.

Other reports said the balloon hit a tree before catching fire, and that some of the passengers jumped out when it went up in flames.

The accident occurred in a field surrounded by forests.

Police said an investigation was underway.

Slovena's Defence and Interior ministers Ales Hojs and Vinko Gorenak both visited the site of the accident Thursday, while President Danilo Turk expressed his condolences to the families of the victims.

He vowed: "All necessary services have been engaged and they will do whatever they can to prevent an increase of the number of victims."