Voetbal24 reports the Hammers are readying an offer for the powerful striker, according to Nigerian media sources.
The Nigeria international joined Genk in 2019 from Denmark's FC Midtjylland and caught fire this season in the Jupiler League.
Onuachu is well aware of the interest and press his form is now attracting and has confessed an ambition to play in England - and for Arsenal - in the future. Standing at 6ft 7in, Onuachu admits there's two great African centre-forwards he models his game on - and both enjoyed success in the Arsenal shirt.
He told Sporza earlier in the season: "I really like Arsenal.
"(Emmanuel) Adebayor is one of the players I have admired the most. I was a really big fan of him and (Nwankwo) Kanu. I really love watching Arsenal."
Onuachu is contracted to Genk until 2024. He has been in Europe since 2012, when FC Midtjylland first brought him to Europe after being impressed by his form with their affiliate team in Nigeria, Ebedei.
Last season, the 2.01m centre-forward scored 35 goals in 41 appearances for Genk.
- updated June 21