"She knew they were bad people trying to break in", he said and added, "She managed to hold the door for a few seconds but they overpowered her".
"Searches of a number of addresses in Barking are continuing", the statement said. All three wee later shot dead by local police at the scene.
"(The man) said he had been stabbed in the neck and I was holding his bandage and wound while he was talking to the police".
May has come under fire from her main challenger for thousands of cuts made to Britain's police force.
There were several police vehicles outside a block of flats that had been cordoned off.
The Metropolitan Police Federation, which represents officers in London, said there were "barely words to describe" the bravery of all officers, armed and unarmed, who responded to last night's incident. The attacker was gunned down by a police officer.
May laid some groundwork for what the British government would do in the wake of the attack: "We cannot and must not pretend that things can continue as they are".More news: Ariana Grande holds benefit concert in wake of terror attacks
More news: PK Subban: Crosby denies comments about Subban's breath
More news: UK election pauses, for second time, after London attack
In Borough Market, a popular nightspot for Londoners and tourists, civilians had to scramble to safety or hide in the places where they were enjoying their night on what was a warm summer's evening.
A witness on the bridge told CNN the van mowed down pedestrians as it sped south across the bridge, leaving bodies lying in the roadway.
Islamic State earlier on Saturday sent out a call on instant messaging service Telegram urging its followers to launch attacks with trucks, knives and guns against "Crusaders" during the Muslim holy month of Ramadan.
Prime Minister Theresa May said: "Our thoughts are with those who are caught up in these terrible events".
"I can't imagine Theresa May tweeting like this to the mayor of Orlando or San Bernadino", said Heye. "The man started screaming and dropping everything on the floor, the plates, the cutlery, the bottle, everything, he dropped it".
One woman, who was in Black and Blue restaurant, said: "We just saw three guys come into the restaurant, stabbed someone in the face and someone in the stomach".
Sky News had previously reported the arrest of four men following a raid by armed police on Sunday morning, as well as one woman who was then released.