By Sebastien Malo

NEW YORK (Reuters) - New York City police were on the lookout on Tuesday for a hammer-wielding man who hit three people on the head, wounding them, in tourist-packed areas.

In one of the three attacks on Monday, a 28-year-old Manhattan woman sitting on a bench in Union Square Park that evening noticed a man sitting across from her, smoking cigarettes, a New York Police Department spokeswoman said. As she walked toward a park exit, he took a hammer out of a bag and struck her with it, police said.

Just 10 minutes or so later, also in Lower Manhattan, a 33-year-old woman who was walking with her boyfriend was approached from behind and hit in the back of the head, authorities said. The suspect fled.

While investigating the assaults, police learned of a third attack earlier in the day in Midtown Manhattan. The victim, a 20-year-old man, had been crossing a street when he was hit in the head with a hammer, police said.

All three victims suffered scalp injuries, including cuts to the head, and were rushed to Lenox Hill Hospital on Manhattan's Upper East Side for treatment.

The two women were discharged. It was unclear whether the man, who was in stable condition when taken to the hospital, was still being treated.

Police said they were investigating the attacks as linked.

(Editing by Barbara Goldberg and Jonathan Oatis)