The liftoff of a test vehicle with crew safety related payloads connected to the ambitious Gaganyaan human space flight mission on Saturday could not happen as planned following an anomaly which will be analysed, ISRO chief S Somanath said.

Engine ignition of the TV-D1 rocket did not happen in the course of time.

After suffering delays twice, totaling 45 minutes, the rocket failed to liftoff from the spaceport here at 8.45 am, even as a "hold" signal flashed across the screens at the Satish Dhawan Space Centre while the final countdown was on.

There was a very smooth air lift and automatic launch sequence leading up to the command to lift off, "but the engine ignition has not happened in the nominal course due to anomaly," Somanath said soon after the mission was put on hold.

"And we have to find out what went wrong with that. The vehicle is safe, the entire vehicle is very safe. We will have to reach the vehicle and then look at what has happened now," he said, adding ISRO will come back soon after analysing what triggered the automatic launch sequence holding the vehicle.

"So what has happened is that the ground support computer doing this function has withheld the launch in view of the anomaly observed. We will come back after understanding the anomaly, correct it and schedule the launch very soon," the space agency's Chairman said from the Mission Control Center.

The revised launch schedule will be announced later after analysing what went wrong today, he added.