A winter storm hammered Toronto and surrounding regions on Wednesday, bringing significant snowfall that caused traffic and transit delays and flight cancellations.

Snow began falling around 10 a.m. and intensified in the afternoon and early evening as many headed home from work and school.

The inclement weather made for a hectic commute during rush hour, with heavy snow slowing down TTC service across the city. On social media, many users posted about waiting for buses for hours. The TTC said many buses were stuck in snow leading to longer wait times.

The transit agency put 41 bus stops located in hilly areas out of service. The TTC also halted service on Line 3 Scarborough due to poor conditions, replacing trains with shuttle buses.

The snow also created dangerous and hazardous driving conditions on local roads and highways. Dozens of collisions were reported across the Greater Toronto Area, according to the Ontario Provincial Police.

"We're dealing with about 40 crashes right now across the GTA," Sgt. Kerry Schmidt told CP24 Wednesday afternoon.

"Fortunately, none of them are reported as any serious injuries… we've got lots of problems; officers are responding as quickly as they can."

Meanwhile, hundreds of flights were cancelled at Toronto Pearson International Airport due to the storm. The airport asked travellers to check their flight status before heading out.

As of 10 p.m., Toronto and much of southern Ontario remain under a snowfall warning from Environment Canada on Wednesday.

The weather agency warned that a Texas low could dump 15 to 20 centimetres of snow between Wednesday afternoon and Thursday morning.

"Prepare for quickly changing and deteriorating travel conditions. There may be a significant impact on rush hour traffic in urban areas," Environment Canada said in its Wednesday afternoon advisory. "Take frequent breaks and avoid strain when clearing snow. Public Safety Canada encourages everyone to make an emergency plan and get an emergency kit with drinking water, food, medicine, a first-aid kit and a flashlight."

The snow also led to some school bus cancellations in the region. School buses were running for public and Catholic schools in Toronto and most of the GTA, however. The York Region District School Board and the York Catholic District School Board have already announced school bus cancellations for Thursday.

Some postsecondary institutions closed their campuses in the afternoon due to the snow, with all in-person and online classes being cancelled.

Meanwhile, the city opened three warming centres for those who need to seek shelter from the storm.

City road crews were out early Wednesday, gearing up for one of the biggest storms of the season so far.

"This is going to be, most likely, the most significant winter event we've had this winter season with respect to snowfall accumulation," Toronto Transportation Services Director of Operations and Maintenance Vince Sferrazza told reporters Wednesday morning.

He said the heavy snow is expected to come quickly and it will likely take city crews multiple rounds of clearing to clean it all up.

"The one thing I want to stress is that this is going to be a multiple round and multiple pass event," Sferrazza said. "The equipment; the salters, the plows, the sidewalk machines for the bicycle lanes, all of them will have to complete numerous rounds throughout the next few days."

The snow is expected to taper off Thursday morning. It will be cloudy with a 30 per cent chance of flurries for the rest of the day. The high will be -1 C with a wind chill near -9.

On Friday, it will remain cloudy with a high of 0 C.

- with files from Jordan Fleguel and Bryann Aguilar