Footage of monkeys screaming in pain inside a German laboratory have been caught on hidden camera video.

Released by animal rights activists, the distressing eight-minute video has prompted calls for a change to European Union laws.

Besides primates, the video also showed household pets such as cats and dogs that appear to be bleeding and even dying after being tested on.

Undercover work

An undercover worker from organisations Soko Tierschutz and Cruelty Free International (CFI) secretly shot the video inside Laboratory of Phramacology and Toxicology (LPT) in Hamburg.

The monkeys were seen crying like newborn babies.

They were hanging from metal harnesses strapped to their necks.

Those in cages were squeezed into tiny spaces, which caused the monkeys to behave in a crazy fashion, such as developing compulsive behaviour where they keeping performing the same movement over and over again.

Toxicology tests were apparently carried out on cats, dogs and rabbits.

The animals appeared to be left in highly distressed states.

Animals subjected to poisoning

According to CFI, the animals were used as test subjects, which involved poisoning them to see how much of a chemical or drug it can tolerate before serious harm is done.

This sort of testing is to measure what a "safe" dose for humans might be.

CFI also claimed the animals were injected with or made to eat or inhale increasing amounts of a substance to measure the toxic effects.

The resultant effects the animals suffer from include vomiting, internal bleeding, respiratory distress, fever, weight loss, lethargy, skin problems, organ failure and even death.

Workers not trained to handle animals

CFI claimed the animals were not given pain relief or anaesthetics prior to testing.

Staff were also witnessed to be not trained to handle animals and were often violent towards the animals.

Beagles were seen bleeding after the experiments involving pipes forced down their throats to feed them capsules.

After the animals were experimented on, they were then disposed of with almost little to no regard.

Friedrich Mülln from Soko Tierschutz said: "The animals were even still waggling their tails when they were being taken to be killed, the dogs were desperate for human contact."

Call for changes in laws

CFI is calling for laws to be changed in the EU.

An online petition has been launched calling for LPT to be shut down.

It has accumulated more than 110,000 signatures since it was launched on Oct. 11.

LPT is a family-owned company that carries out toxicity testing for pharmaceutical, industrial and agro-chemical companies globally to ensure products meet the requirements of governments and regulatory authorities.

Warning: Some viewers might find the following footage distressing.