A Dutch passenger train derailed after smashing into a crane early on Tuesday, killing a maintenance worker and injuring 30 other people in the Netherlands' worst rail accident for years.

The double-decker train carrying around 50 people from Leiden to The Hague veered off the tracks near the village of Voorschoten at around 3:30 am (0130 GMT), ending up partly in a field.

The Dutch infrastructure minister said it was a "miracle" that more people had not been killed in the crash, in which a freight train also hit the crane as it made overnight repairs on two out of four tracks.

King Willem-Alexander later visited the site of the crash, where one of the damaged yellow and blue passenger carriages lay in a meadow while the three others were strewn across the rails.

It was 'a miracle' that more people were not killed in the train derailment, officials said.

People living near the scene, around eight kilometres (five miles) north of The Hague, helped the victims and let medics treat the injured in their homes.

"We heard a bang first and then later a much more intense one," local resident Chris van Engelenburg, 36, told AFP.

"Then we heard people screaming. It was not good."

The dead victim was an employee of rail maintenance company BAM, the firm said.

Thirty people were injured, with 19 taken to hospital and 11 treated at the scene, emergency services confirmed.

- 'Black day' -

Dutch police and prosecutors said they had launched a criminal investigation, while rail authorities and the country's safety board are probing the cause of the crash.

The head of the rail network company ProRail, John Voppen, said it was a "black day for the Dutch railways".

Maintenance work involving the crane was underway when the crash happened, with two out of four tracks in the area being out of use.

"We really don’t know what happened," Voppen told a press conference.

The head of Dutch train operator NS, Wouter Koolmees, said the "devastation is very big". The driver of the passenger train was in hospital with bone fractures, he added.

Emergency services described a "chaotic situation" with rescue workers having to use wooden boards to get across a narrow canal, while watching for danger for damaged electrical cables.

Video taken by one passenger shows people using mobile phone torch-lights as they tried to smash their way through emergency exits, while voices can be heard shouting "leave the train".

Local resident Jaron Ooms, 45, said it was "really scary".

"We heard a very loud bang and for sure the house started to shake heavily," Ooms told AFP. "We did hear people screaming and at one point I also saw people with telephones searching in the meadow."

- 'Speechless' -

King Willem-Alexander, wearing an orange high-visibility vest, spoke to emergency workers and walked along the tracks when he visited the scene.

"I'm just speechless right now seeing this," said the Dutch monarch.

The wreckage of the crane could also be seen further down the line.

Prime Minister Mark Rutte described it in a tweet as a "terrible train accident".

No trains will run from Leiden to The Hague for the rest of Tuesday and services will be disrupted for several days. 

But international Eurostar trains linking Amsterdam with London and Thalys services to Brussels and Paris were unaffected.

The accident was the most serious in the Netherlands for years, according to public broadcaster NOS.

The Netherlands' worst train disaster happened on January 8, 1962, when two passenger trains crashed after a driver missed a signal in thick fog at Harmelen, near the central city of Utrecht, killing 93 people and injuring 52 others.

One person was killed and six others were injured when a train collided with a hydraulic crane in central Netherlands in 2016. 

Another person died and 117 others were injured in a collision near Amsterdam in 2012 with reports later saying a driver failed to respect a stop sign.