Lupita Nyong’o has written an opinion piece for the New York Times, detailing several encounters with Harvey Weinstein in which the producer allegedly offered to help her career in exchange for sex.

The 12 Years a Slave actor wrote that she “felt sick in the pit of [her] stomach” after allegations by more than 50 women became public and she realised her alleged treatment was part of a “sinister pattern of behavior”.

In the piece, Nyong’o said she first encountered Weinstein while she was a student attending the Berlin film festival, where she was at a dinner with the producer.

Shortly afterward, she was invited to a screening at his home in Westport, Connecticut, after a dinner where Weinstein had become angry when she refused to drink a vodka and diet soda. After the dinner, the actor claimed, while Weinstein’s young children were watching a film, he asked Nyong’o to leave the room and let him give her a massage.

“I began to massage his back to buy myself time to figure out how to extricate myself from this undesirable situation,” she wrote. “Before long he said he wanted to take off his pants. I told him not to do that and informed him that it would make me extremely uncomfortable. He got up anyway to do so and I headed for the door, saying that I was not at all comfortable with that.”

The actor said she “didn’t know how to proceed without jeopardizing my future”, and invited Weinstein to see a production at Yale School of Drama. He could not make it but instead invited Nyong’o to a Broadway production. Nothing happened on that occasion but the next time they met – at a dinner in TriBeCa, New York – Weinstein propositioned her, the actor said.

“If I wanted to be an actress, then I had to be willing to do this sort of thing,” she wrote. “He said he had dated Famous Actress X and Y and look where that had gotten them.

“I had shelved my experience with Harvey far in the recesses of my mind, joining in the conspiracy of silence that has allowed this predator to prowl for so many years. I had felt very much alone when these things happened, and I had blamed myself for a lot of it, quite like many of the other women who have shared their stories.”

After Nyong’o’s success in 12 Years a Slave – a role which won her an Oscar in 2014 – she said Weinstein continued to pursue her and offered roles in his productions. She turned the offers down, she said.

“I was so exasperated by the end that I just kept quiet. Harvey finally accepted my position and expressed that he still wanted to work with me at some point. ‘Thank you, I hope so,’ I lied.

“Wherever I looked, everyone seemed to be bracing themselves and dealing with him, unchallenged,” she added. “I did not know that things could change. I did not know that anybody wanted things to change. So my survival plan was to avoid Harvey and men like him at all costs, and I did not know that I had allies in this.”

On Thursday, Quentin Tarantino said that he had been aware of alleged assaults by Weinstein and said he wished he had done more to help women affected.

“There was more to it than just the normal rumors, the normal gossip,” he said in the interview with the New York Times. “It wasn’t secondhand. I knew he did a couple of these things.

“I wish I had taken responsibility for what I heard. If I had done the work I should have done then, I would have had to not work with him.”