“The train stopped for a long time and there was an announcement about signal failure, but I didn’t realize anything strange was going on until later,” Chase-Levenson wrote in an e-mail.

“Fortunately, I had decided to walk to a different tube stop rather than changing at King’s Cross which I often do,” he said.

Ruthie B. Birger ’06, who lives two tube stops from King’s Cross, wrote in an e-mail that “when I got to the [Finsbury Park] station there was an announcement that it was [closed] and that we should take the buses....At the time I thought it was only my tube station that was closed but as the bus drove through north and central London I saw hundreds of people waiting at the stops so I realized something else was going on.”

At 9:17 a.m., there was a third explosion involving two or three trains around Edgware Road station. Seven people were killed in that attack, police said.

The fourth and final attack, on a double-decker bus, came at 9:47 a.m. near Russell Square, killing at least two, according to the police.

The attacks came only a day after the start of a G-8 summit in Scotland attended by several heads of state, including Blair and President George W. Bush. Blair rushed back from the summit to London for emergency meetings, appearing in a televised address later that afternoon calling the day “a very sad day for the British people.”

BOSTON RESPONDS

Shortly following the attacks in London, Massachusetts Governor Mitt Romney met with state transportation officials, ordering the Massachusetts Bay Transit Authority (MBTA) to increase security system-wide, marking the first such security upgrade in the state since last summer’s Democratic National Convention.

MBTA police inspected tracks, out-of-service trains, and buses for bombs; recordings played over speakers at Park Street directed commuters to report suspicious behavior or packages.

Later in the day, the Department of Homeland Security raised the threat level for the nation’s transit systems to code orange, which is the second highest level of alert. Although officials had received no specific threats against U.S. cities, Homeland Security Secretary Michael Chertoff said that he remained “concerned about the possibility of a copycat attack.”

HARVARD TAKES ACTION

Thousands of miles from London, officials at Harvard, watching television news reports of the London blasts for the first time, rushed to contact every Harvard student they believed to be in the London area.

The University has no central database listing students’ summer locations, and not all students in London are necessarily registered through Harvard. Students can work or attend classes abroad under the auspices of many University offices, including the Office of International Programs (OIP), the Office of Career Services (OCS), the Minda de Gunzburg Center for European Studies (CES), and the Summer School. Officials from several of these programs worked together Thursday to contact all of the students believed to be in the London area, as well as those believed to have plans to travel to London later in the summer.