According to Gazzetta dello Sport, the two London clubs also face competition from Nice, who are reportedly keen on replacing striker Mario Balotelli.
Niang may be familiar to Premier League fans after his brief loan spell at Watford. The loan was not particularly successful, however, with the 23-year-old managing just two goals in 16 appearances for the Hornets.
The Senegal international has also spent time on loan in Italy and France, where he has enjoyed greater success. Whilst at Genoa Niang scored five goals in 14 appearances, but his loan was cut short after suffering an injury.
Niang is understood to favour a move to France and is quoted in the report as saying: "After the holidays I will evaluate what is best for me, I like the idea of embarking on new experiences.
"Where is it? I could not express myself in France, I would like to come back, even for family reasons, I know several clubs in Ligue 1 follow me: it's definitely a possibility."
Unai Emery is reportedly interested in signing a fast, direct winger and Niang certainly has the attributes to play in that role. However, the Arsenal boss has already spent a substantial amount this window.
West Ham have also been busy this transfer window as new manager Manuel Pellegrini looks to reshape his squad ahead of the new season. Fans will be delighted that the Hammers are spending money after many felt that the club under achieved last season.