Party-goer O'Brien Morrison said he and a friend felt forced to leave the property, in Willows Road, Walsall, in fear of their safety.
Rezwan Ali, 19, was knifed three times in the kitchen following a dispute between two different groups on January 14, 2018.
Mr Morrison, referred to as Demarai, also told Birmingham Crown Court his phone went "missing" at the party.
He said: "Downstairs felt toxic. It didn't feel a good environment. I didn't know anyone. The people looked aggressive.
"My phone went missing when I came to collect it on charge. I raised my voice and asked if anybody had seen it.
"Within 10 minutes it was in a cupboard. Someone passed it to me.
"I left about five minutes after before anyone got injured. We left around 10pm [the day before]."
The trial so far:
Demarai said his friend, who organised the party, told him the house was "getting wrecked and out of control".
He said this prompted him and another friend to leave as they "didn't feel safe". "I heard about the stabbing when I got home," he said.
Mr Ali, a pizza deliver driver, suffered a fatal stab wound to his chest which pierced his heart.
Rajan Natt, 20, of of Castle Street, West Bromwich, is accused of Mr Ali's murder. He denies any wrongdoing.
Asked by Mr James Curtis QC, prosecuting, if everyone had been behaving, Demarai said: "Their behaviour was peculiar.
"They were very loud. It wasn't the normal type of people I would associate myself with."
He estimated there were around 50 people at the party.
Jurors were told the event had been organised for 10 people originally, but many more turned up as it was advertised on social media.
Asked about the ethnicity of people at the party, Demarai said: "Ninety per cent of the party was Asian.
"The others were black. There was also some white people."
'He started gasping for air'
Ayoub Elbadr, who also attended the party, said a man stumbled past him bleeding before he collapsed on the floor.
At first, Mr Elbadr thought this man was drunk until he saw the injured man's blood on his own trainers and jeans.
Mr Elbadr told jurors: "As he walked past me, some of his blood dripped onto my jeans and shoes.
"He carried on walking towards the kitchen before he just collapsed. He started gasping for air."
Jurors were told a "brawl" took place in the garden area earlier that night between two different groups of friends.
Mr Elbadr said one group was more aggressive than other but the fight lasted no more than 30 seconds.
A taxi driver called Rubel Ahmed also gave evidence, where he recalled picking up six passengers at Toby Carvery, Walsall, at around 02.48am.
Mr Ahmed, who was employed by Choice Cars, in Wednesbury, said the passengers were Asian and aged between 18 and 20.
He told the court they appeared somewhat panicked.
"One of them asked for a tissue because his nose was bleeding," said Mr Ahmed.
The court heard he went to Oldbury police station in the wake of the stabbing where officers "did some sort of check" on his taxi, he said.
The trial continues.