DENVER - Denver police say four people were set afire during an assault in North Denver Thursday night.

The incident happened in the 4300 block of Lipan Street shortly before 7:30 p.m.

Police spokeswoman Raquel Lopez said two black males knocked on an apartment door and when a woman answered, she was sprayed with some type of liquid from a lawn and garden sprayer.  The woman was then set afire when the men threw a match or lighter on her.

Lopez said the initial report of a small propane torch being used was incorrect.

Three others -- two men and a second woman -- inside the apartment were also sprayed and set afire, but suffered only minor burns, she said.

Lopez said the woman who answered the door was the most seriously burned and she was transported by ambulance to a local hospital. 

Police do not have a motive for the attacks but they called the incident "highly unusual and extremely scary."

Police were trying to get better descriptions of the suspects.

Police are also investigating an earlier robbery with flammable liquid used at a check-cashing service at 32nd and Champa streets, in the Curtis Park neighborhood.

Witnesses told 7NEWS that two men entered the Ace Check Cashing and stuck a tube through a cash portal and sprayed a flammable liquid on the counter inside the protective glass, then lit it.

"We noticed the smell, it smelled like burning plastic," said one of two men who was in the area. "We came around to the front of the building and noticed ... an employee of the check cashing business and she was trapped in the enclosure where she worked -- there was a cloud of smoke and the counter was on fire."

The woman who was working in the secured area was not injured but was quite distraught, the man said.

The two suspected robbers were last seen running from the business.

Police have not yet linked to the two incidents.