LONDON, England (CNN) -- Flight cancellations, delays and baggage problems continued to plague Heathrow Airport's Terminal Five for a second day, causing more headaches for passengers just a day after the much-heralded building opened for business.

British Airways, the only airline operating from the new terminal, canceled 20 percent of its flights from the terminal on Friday, a spokesman said, and predicted possible delays for the remaining 80 percent.

The airline later said passengers could check in luggage with normal luggage restrictions in place.

The problems came after a disastrous first day for the terminal during which the entire baggage system -- designed to handle dozens of planes at the same time and process 12,000 bags an hour -- failed.

CNN's Richard Quest said: "The news is simply grim at Terminal 5. It couldn't have happened at a worse time."

British Airways and UK airports operator BAA had spent two decades and $8.6 billion building the terminal.

BAA was banking on the luggage system to improve a reputation for chaotic handling that had helped the airport west of London earn the nickname "Hassle Heathrow."

BA director of operations Gareth Kirkwood said: "We sincerely apologize to those customers who have suffered disrupted journeys or baggage delays. We always knew the first day would represent a unique challenge."

Initial glitches in the baggage handling led to the cancellation of at least 34 flights on Thursday. BA earlier admitted some "teething problems" had caused incoming or outgoing flights to be canceled.

"It's almost open," Jeff Bryan joked after he and his wife spent 90 minutes waiting for their luggage after an overnight British Airways flight from Miami to Heathrow. "We didn't mind because we're not in a rush, but a lot of people were," he told The Associated Press.

Adding to the opening day woes were protests by campaigners opposed to the airport's expansion.

Later a "flash mob" protest, involving several hundred demonstrators opposed to airport expansion, took place at T5. CNN's Richard Quest, describing the protest, said the day had started out well for BAA but was turning into a "shambles."

The protesters stripped off their outer clothes at 11 a.m. to show red T-shirts emblazoned with the slogan "Stop Airport Expansion."

Made up of local residents and environmental groups, the demonstrators are concerned that a third runway and a sixth terminal will be created at Heathrow, the world's busiest international airport.

Supporters say expansion of Heathrow is vital for the city's economy. Environmentalists say though that expanding London's three main airports -- Heathrow, Gatwick, and Stansted -- will only add to harmful climate change.

The new terminal frees up the rest of Heathrow for other carriers, who are eager to offer services to one of the world's busiest international hubs.

A new agreement, called OpenSkies, comes into force this weekend meaning that travelers on both sides of the Atlantic have more options when booking nonstop flights between the U.S. and Europe.