A woman died and three people were sent to hospital after a GO Transit bus rolled over on Highway 407 near Weston Road just north of Toronto on Wednesday night.

The single-vehicle crash happened at about 10 p.m. ET when the bus hit a guard rail then rolled onto its passenger side. The OPP say 56 year-old Radika Nankissoor of Brampton, Ont., died in the crash.

York University said Thursday that Nankissoor was a custodian at the school and had worked there since 2010.

In a statement, York president and vice chancellor Mamdouh Shoukri said the York community is "deeply saddened" by her death.

"We extend our deepest sympathy to her family, friends and co-workers at this difficult time," Shoukri said in the statement.

The bus came to a stop in a grassy area between the Highway 407 and a ramp for Highway 400.

"A portion of that guard rail actually entered the compartment inside the bus," Ontario Provincial Police Staff Sgt. Kerry Schmidt told CBC News. "And some of the guard rail went off to the side."

The bus was travelling east on GO route 47 from Hamilton to York University. The provincially owned GO Transit operates bus and train commuter service between Toronto and its surrounding suburbs and cities.

Six people were aboard, including the driver.

Three people were taken to hospital and treated for injuries not believed to be life-threatening. Among them is the driver, a 66-year-old Hamilton man. Two other passengers were not hurt. One woman injured is a York student, according to the university while another hurt in the crash is an alumnus of the school.

Schmidt said it's fortunate there were only five passengers on board.

"It could have been far worse had the bus been loaded to capacity," he said.

The OPP, in co-operation from Metrolinx —  the agency responsible for GO Transit — will investigate what caused the bus to veer off the highway.

Authorities initially believed that a male passenger died at the scene, but hours later after the bus was lifted, it was revealed that the person was a woman. Police say she was thrown from the bus during the crash and pinned beneath it.

Metrolinx said the driver is an experienced operator who is co-operating with the investigation. They also say there was no apparent medical condition that may have led to the rollover. Police say they don't yet know what may have caused the bus to crash.

Police believe the bus was the only vehicle involved in the crash.

At a news conference Thursday morning, GO Transit president Greg Percy extended his condolences to Nankissoor's family. He said safety remains a priority for GO, which carries some 65 million passengers a year over its bus and rail network.

Percy said the bus is not equipped with an on-board camera, but does have a diagnostic computer that could provide investigators with information about the bus's speed and braking at the time of the crash.

"We will continue to place safety as the highest priority for GO Transit," he said. Percy said this is the first time a passenger has died aboard a GO bus or train.

The eastbound Highway 407 ramp to Highway 400 was closed while police investigated the crash overnight. Just after 6:15 a.m. ET Thursday, the OPP announced it had reopened.

GO TRANSIT BUS CRASH
With files from Tony Smyth