“The priests who live on the fifth and sixth floors are fine. We are trying to locate a volunteer who works with us,” the vicar general told Telemadrid.
A reporter for TVE public broadcaster said several had been injured, without giving details.
Emergency services could not immediately confirm if there had been injuries.
A Reuters reporter saw smoke coming out of the collapsed building and rescue workers evacuating elderly people from a nearby nursing home.
The collapsed building was a religious complex that provided residential training for priests and gave meals for the homeless, a neighbour told Reuters.
A police spokeswoman said the area was being evacuated but could not confirm the source of the explosion.
La Sexta TV quoted government sources saying it may have been a gas leak. Officials could not immediately confirm.
The explosion happened in Toledo street, in the city centre. (Reuters/NAN)