A woman was killed and four others were left critically injured after two recreational boats collided on Lake Michigan near downtown Chicago, but investigators have yet to answer many of the questions surrounding the late-night crash.

Johanna H. Gregory, 26, died after the collision involving 14 people near Monroe Harbor around 11.45pm Thursday, according to the Cook County Medical Examiner's Office.

Five people were rushed to hospitals in serious to grave condition while nine others declined medical treatment, the Chicago Fire Department said.

Authorities have released only a preliminary account of what happened, with the Illinois Department of Natural Resources now leading the investigation.

According to the Chicago Fire Department, both recreational boats were returning to port about 1.5 miles from shore when one vessel overtook the other, causing the collision.

One boat was carrying nine people while the other had five passengers. Those aboard ranged in age from 18 to 26, according to ABC7 Chicago.

Two people were thrown into the water during the crash but were pulled to safety by others aboard the boats before first responders arrived.

Emergency crews reached the scene within seven minutes of receiving the initial call, officials said.

Three injured passengers were taken to Northwestern Hospital while two others were transported to Stroger Hospital.

Gregory, a Chicago resident from the city's West Loop neighborhood, was later identified as the woman who died from injuries sustained in the crash.

Gannon University, where Gregory played volleyball, remembered her as a 'beloved member of our volleyball program and Gannon family.'

The Coast Guard towed one boat to Queen's Landing across from Buckingham Fountain. Chicago police towed the other vessel, which suffered the most damage, to the department's Marine Unit headquarters.

Chicago Fire Department Deputy District Chief Jason Lach said preliminary information indicated both boats had been returning to shore when the crash occurred.

'Two vessels were coming back into port,' Lach said. 'We are not exactly sure if they were both coming back in here to Monroe Harbor or Burnham Harbor. One vessel overtook another one, and there was a collision that happened.'

Investigators have established a basic timeline but have yet to determine what caused the collision.

Officials have not identified the operators of either boat or disclosed who was at the helm when the vessels collided.

Authorities also have not said why one boat overtook the other or whether excessive speed contributed to the crash.

Investigators have not determined whether alcohol or drugs played a role or whether either operator underwent toxicology testing.

Officials also have not established whether both boats had their required navigation lights illuminated at the time of the collision.

It also remains unclear whether everyone aboard was wearing life jackets or whether mechanical problems contributed to the crash.

Investigators have said lake conditions did not appear to have been a factor.

The Illinois Department of Natural Resources is leading the investigation, and the Chicago Fire Department said everyone involved has been cooperating with investigators.

'While the circumstances are under investigation, this serves as a sobering reminder that safety on the water begins long before leaving the dock,' Coast Guard Lieutenant Commander James Alling said in a statement.

'Boaters should always wear a life jacket, maintain a proper lookout, operate at a safe speed, and never operate a vessel under the influence. Taking these simple precautions can make the difference between a close call and a tragedy.'

Authorities have not announced any citations or criminal charges, and have not said when they expect to release additional findings.