A police commander who took control after the Manchester Arena attack has described his frustration at being unable to contact emergency services.
British Transport Police (BTP) Insp Ben Dawson was based in a London control room on the night of the explosion.
Insp Dawson said the control room could not contact other police and ambulance services and his team had to ring 999 and wait in a queue with the public.
He told an inquiry the first hour after the bombing was "absolute chaos".
BTP officers were the first emergency responders at the scene after Salman Abedi detonated a device at the end of an Ariana Grande concert on 22 May 2017.
Twenty-two people died and hundreds more were injured.
The BTP control room was first made aware of the incident 68 seconds after the explosion.
Giving evidence to the public inquiry into the atrocity, Insp Dawson said one of his urgent priorities was to speak to his equivalent at Greater Manchester Police (GMP) but he was unable to get through to him.
"I didn't manage to speak to him at all throughout the whole incident," he said.
"I was certainly frustrated. It would have helped a lot."
The police commander also said his colleagues, who were based in a separate control room in Birmingham, had no direct line for GMP and the North West Ambulance Service (NWAS).
In the minutes after the attack, he said his colleagues had to wait in a call queue with the public.
Insp Dawson told the inquiry there was now a direct phone line set up between BTP and GMP.
The hearing was told there was no CCTV link to the control room so Insp Dawson said his main source of information was BTP officers on the ground.
The inquiry has previously heard how the GMP Force Duty Officer was overwhelmed during the aftermath of the bombing.
Insp Dawson said the co-ordination of emergency services "was not cohesive, in terms of working together".
"We weren't working together as well as we could have done," he said.
However, the commander said he believed BTP had done its best to work with other responders and said he felt sufficiently trained for his role.
The inquiry chair, Sir John Saunders, asked Insp Dawson whether responding to an attack such as the arena bombing would always be chaos because it was "such an appalling incident".
"It's the art of turning chaos into an organised response," Insp Dawson replied.
"That's what we're paid for, that's what were trained for, but it is very, very difficult."
The inquiry continues.