KIEV, July 18 - Scores of people sought medical help on Wednesday after a poisonous chemical spill in Ukraine, Greenpeace said, warning of dangers to health and the environment from the toxic fumes, Reuters reported.

The environmental campaign group said 16 people were taken to hospitals on Tuesday and another 55 sought treatment on Wednesday. Neighboring countries also expressed concern.

The Ukrainian Health Ministry said 19 children were among those hospitalized.

But Ukrainian officials sought to play down the dangers from the fumes released after highly poisonous phosphorous caught fire following a train derailment in western Ukraine on Monday, spreading a toxic cloud over 90 sq km.

Hundreds of people were evacuated from nearby villages, with up to 11,000 residents close to the site anxiously hoping the contamination doesn't spread.

"This is a dangerous substance ... It is highly flammable and causes burns and choking," said Alexei Kiselev, a Greenpeace Russia toxic expert. He predicted it would take a long time to clean up the spill.

The European Union said it was on standby to offer Ukraine assistance with aid ranging from field hospitals and aircraft to help with evacuations, if required.

Warning the toxic cloud would not respect borders, the European Commission said it was monitoring its movement.

"The EU is ready to provide assistance, but so far there has been no request from the Ukrainian authorities and we can only act if they request it," said spokeswoman Barbara Helfferich.

"We are trying to monitor the situation, through the Ukrainian, Polish and Romanian authorities," she said.

A cargo train, en route to Poland from Kazakhstan, derailed, releasing the gas from six tanks and generating a fierce fire.

Witnesses, including an official traveling on the train, said they heard a loud bang just beforehand.

Investigators said they were still working to establish the cause of the incident near the ancient gothic city of Lviv, close to the Polish border.

"Experts from Kazahkstan have now arrived at the scene and are trying to work out what happened," Ihor Krol, the emergency ministry spokesman told Reuters.

Ukraine's efforts to handle the disaster are being hampered by a lack of local expertise in dealing with environmental threats, officials conceded.

In Lithuania, the Foreign Ministry advised its citizens to avoid the whole of western Ukraine as a precautionary measure.

"It's a very dangerous substance which affects the nervous system, the human metabolism and even the blood structure, it is poison," Valiriya Morkunene, head of the chemistry department of the Health Environment Centre in Vilnius, told RIA news agency. (rt/ez)