A technical issue is being blamed for halting SkyTrain service between downtown Vancouver and New Westminster Tuesday, trapping hundreds of people on muggy trains.

TransLink said 19 trains somehow lost communication with its control centre around 4:20 p.m., while many were packed full with rush hour commuters.

Attendants were quickly dispatched to all of the trains, and 17 were manually returned to stations and evacuated within about an hour-and-a-half.

The other two were potentially delayed because some passengers pried doors open and walked onto the SkyTrain guideways, as many did during similar outages last summer.

“Unfortunately when that happens that causes further delays because you can’t even manually bring trains though on a system where you have people on the guideway,” spokeswoman Anne Drennan said.

Drennan said she understands that people may have been frightened due to the heat, but TransLink's response was "much more refined" than it was last summer.

“Attendants and Transit Police officers head out to the trains almost immediately so contact is made and they can assure people that we know where they are,” she said.

One pregnant passenger suffered an anxiety attack during the shutdown. TransLink said her train was brought into a station as quickly as possible and she was met with ambulance attendants.

It’s unclear what caused the 19 trains to lose communication with TransLink’s control centre, but the issue is being investigated.

Drennan said it doesn’t have any apparent relation to other recent shutdowns.

“The last one was as a result of a spark in a bird’s nest that burned out cables. Before that we had a switch issue, and this is a technical issues involving computer problems,” she said. “So they’re all different issues, things that crop up on systems of this size.”

Crews had service back up and running before 7 p.m.

During the shutdown, shuttles were dispatched to move passengers between Waterfront and Edmonds stations, though many people were still stuck with lengthy delays.

TransLink said Expo Line service between Edmonds and King George stations wasn’t halted, nor was Millennium Line service from Columbia to VCC-Clark stations.

The service provider is expected to provide more information on Wednesday afternoon.