Teachers and friends have paid tribute to a "bright and popular" schoolgirl who was stabbed to death on a crowded bus in Birmingham during the morning rush hour.

Christina Edkins, 16, was on her way to school in Halesowen on Thursday morning when she was attacked. A 22-year-old man has been arrested on suspicion of her murder.

"This is a tragic case and the victim's family are devastated," said Det Supt Richard Baker, from West Midlands police. "We are still anxious to hear from anyone with information or who may have witnessed the incident this morning.

"There will be a high police presence across the city following this morning's tragedy, particularly on buses and in schools in the area to provide reassurance to local people."

Photograph: Phil Barnett/PA

Police officers responded to a call from a member of the public reporting that a passenger had been attacked on Hagley Road, in Birmingham city centre, shortly after 7.30am. An emergency doctor and paramedics from West Midlands ambulance service also arrived but Christina was pronounced dead at the scene. She was on her way to Leasowes high school when the attack took place.

Headteacher Neil Shaw said: "Christina was a bright and popular student much loved by staff and students alike. We are deeply saddened to hear this tragic news and our thoughts and hearts go out to her family and everyone who knew her."

Police officers stood guard at the Edkins' semi-detached house near Birmingham city centre for much of the day while family liaison officers sought to comfort relatives.

The Most Rev Bernard Longley, archbishop of Birmingham, sent his condolences in a message from Rome. "I am shocked to hear of the terrible attack on young Christina Edkins as she was making her way to school on a bus today," he said.

"The loss of a young life in these tragic circumstances raises many questions about our respect for life and about safeguarding children in public places."

A tribute page was set up in her memory on Facebook. Dannie Leigh wrote: "Spent all weekend with the most sweetest girl, and it was only two days ago that we were arranging another catch up r.i.p christina, I love you beautiful." Police said family liaison officers were supporting Christina's family. Counsellors were available to pupils and staff at her school.

Last night flowers were also left near the scene of the stabbing.

On one bunch of roses, a card read: "Christina a truly lovely young girl. We'll miss you. Rest in peace angel. Cass and Ben"

On a bunch of mixed flowers the message on the card read: "To Christina. We will miss you loads. You were a beautiful girl and a bundle of joy. Rest in peace cutey. Lots of love Ryan and Dale xxx".

Another message simply read: "Christina. Gone but never forgotten. Love you loads. Broddersz xxx"

West Midlands police issued a description of the attacker based on witness accounts after the incident and called in firearms officers and police dogs to assist with the search. A man was later arrested following a chase. He was reported to have been detained after being seen acting suspiciously near a Morrison's supermarket.

Earlier, police briefly detained another man in connection with the stabbing but he was released without arrest.

Baker said police were investigating the possibility that the killing was a random attack, adding: "We're looking at a number of motives at the moment."

Police were not looking for anyone else in connection with the killing.

It emerged that Christina had tweeted a month ago about a man "worrying" her on the bus. She wrote: "This man is worrying me on the bus keeps getting up and walking up and down stairs, and sitting in different place."

Less than 24 hours before she was killed, she tweeted: "Why can't something go right for once?" Police said they were looking at Christina's social media footprint but added: "At this stage there's nothing to suggest she was targeted."

They said the suspect was already on the bus when she boarded and there was "nothing immediately" to suggest the two knew each other.

Police tape sealed off the scene of the stabbing and detectives were working alongside specialist forensic investigators to identify CCTV systems that might have captured the incident on camera.

A National Express West Midlands spokesman said: "We can confirm that a tragic incident took place on a No 9 service on the Hagley Road this morning.

"Our thoughts and condolences are with the family of the person involved and we will offer all possible support to the police in their investigation into the matter."